Hyundai and Kia added official GrapheneOS support to their apps months before Volkswagen banned GrapheneOS:

https://discuss.grapheneos.org/d/31697-myhyundai-app-has-official-grapheneos-support

Pressure from Volkswagen customers on them can achieve the same thing. There's no legitimate reason to ban GrapheneOS so they'll undo it with pressure.

myHyundai app has official GrapheneOS support - GrapheneOS Discussion Forum

GrapheneOS discussion forum

GrapheneOS Discussion Forum
Leave a 1 star review for Volkswagen's apps on the Play Store asking them to stop banning GrapheneOS. Explain it's a far more secure operating system and fully possible for them to verify the hardware, OS and their app on it if they insist on doing it. It's far more secure than anything they allow.
Google has misled companies about what the Play Integrity API provides. It doesn't genuinely enforce having a secure device or legitimate app, it only pretends to. It leaves huge security holes open. It enforces Google's business interests and bans having a reasonably secure device with GrapheneOS.

Most companies are unlikely to stop using the Play Integrity API but most are willing to start permitting GrapheneOS via hardware attestation with enough pressure.

In addition to every user of their app on GrapheneOS leaving a 1 star review on the Play Store, multiple other steps can be taken too.

Every GrapheneOS user with one of their cars using the app should file a customer support request. Keep answering them and countering the template responses. Escalate the request higher up. Tell them you want money back for the vehicle due to reduced functionality after the fact and insist on it.
They can trivially stop enforcing the anti-security and anti-competitive Play Integrity API or easily add hardware-based verification of GrapheneOS. Link to https://grapheneos.org/articles/attestation-compatibility-guide in the customer support request, but don't add any links to Play Store reviews to avoid filtering.
GrapheneOS attestation compatibility guide

Guide on using remote attestation in a way that's compatible with GrapheneOS.

GrapheneOS
A bunch of apps have added explicit support for GrapheneOS due to pressure from our users. Our userbase is rapidly growing and we'll gain the ability to apply massive pressure to companies doing this. We plan to ship a feature for our Info app for people to opt-in to getting asked for their help.
GrapheneOS is production quality OS from a non-profit paying around 15 people to work on it. It's far more secure than anything supported by the Play Integrity API. We have an official partnership with Motorola and we'll have more. Just counter template responses and insist on compensation or a fix.
@GrapheneOS Kia app stopped working on graphene after the latest update though :/
@GrapheneOS latest update to the kia app that is
@ellsinger @GrapheneOS maybe contact Kia about it? Might be a bug or something else not intended
@spacebug @GrapheneOS I will if it persists, just haven't had time
@ellsinger @spacebug Kia app is meant to work now but the anti-tampering stuff done by these apps is fragile and they might have broken it again.
@GrapheneOS works now after the latest graphene os update!
@GrapheneOS
Yes! GrapheneOS is great! The Team behind it too... But it is good to mention, that it is AOSP based... And AOSP code is not just 15 people work.
Simmilar to OxygenOS or NothingOS. It is more like distribution than the separate OS. Realy good, polished and hardened distribution of Android.
GrapheneOS, OnePlus or Nothing are still havy based on AOSP and the changes/patches that are for all Android OS'es and that are not a result of only 15 people work.
P. S. I apriciate your work!
@GrapheneOS Done ✅
@Alex2ander It would likely make sense edit it to be more directed to them as a request instead of talking about what they should do for other people reading it. It's fine as is though.
@GrapheneOS Hi Team,
Please reconsider your Play Integrity API policy to allow secure custom operating systems like GrapheneOS.
GrapheneOS fully supports hardware-backed remote attestation and production-signed builds. It is often more secure than stock Android. Relying on strict Google integrity tiers blocks privacy-conscious users while creating a false sense of security, as it doesn't guarantee a vulnerability-free device.
Please adjust your app policy to permit verified, secure hardware.

@GrapheneOS Looking forward to see what comes from your work with Motorola (current and past phone have been Motorola for last nine years).

Interested to hear what other collaborations are in the pipeline too.

@GrapheneOS But can Motorola partner with GrapheneOS without being kicked out by Google from their ecosystem? I understood that Google required that all their stuff was installed on all Android phones from a given manufacturer?
I'd be happy if that is wrong, though.
@dl2jml Google doesn't directly require that but they do make it hard for Motorola to sell devices with GrapheneOS. It doesn't mean it can't be fully worked around. It's also worth noting that Google's licensing model for Google Mobile Services is clearly highly illegal and has already been found to be illegal by the courts in multiple countries including South Korea. Samsung has their own unique agreement with Google now without the same restrictions and other countries should force the same.
@GrapheneOS So, technically I am wrong but only a little bit. Thank you for the answer!
@GrapheneOS i dont know If the Fairphone 3 is supported, but i would love to Switch to graphene, after the Support ran out

@BigDvsRL GrapheneOS is not an OS to use on end-of-life devices. It's a production quality OS with far stronger privacy and security than standard AOSP and especially regular Android devices.

Fairphone 3 is an insecure device on an insecure end-of-life Linux kernel branch for years already. Fairphone misses many standard privacy or security patches. The ones they provide come many months late. It was also missing important hardware-based security features at launch and is missing far more now.

@GrapheneOS yeah, noticed that after googling 😓

@GrapheneOS

I didnt understand what you meant by the opt in feature you explained. Do you care to explain more in depth what you meant?

With kind regards

@flotmjor938382 Our Info app will have toggles to opt-in to receiving different kinds of requests for help from us such as requests for help testing certain apps, carriers, etc. We could make it so people can opt-in to receiving a request for help testing if their carrier is on a list of carriers we need help testing with through the Info app checking if it's relevant to them. Similarly, it could detect if people can help with testing an app or pressuring the app devs to unban GrapheneOS.

@GrapheneOS

I see, sounds like an good idea if the resources are their.
Thank you for the reply.