@kevinteljeur @signalapp
Going forward, I am assuming you would be reinstalling Signal on a new device if "exporting chats" is the issue. Should be possible to simply install Signal on a new phone with the old phone number and your Signal PIN. At a minimum you get your groups back going forward.
The reason this doesn't give you back previous chat data is Signal doesn't store it, your device does. This is what's for security reasons as well as keeping Signal from being forced to spend vastly more on storage.
Note that there are probably more than enough differences between Android and iOS to make creating a program that can run on both at once and make them transfer internal data between each other difficult. That would be true even without Apple's interference. Note that moving existing data from Android to iOS is also not supported, this is probably why.
I have myself never used export of data directly from Signal. Any photos inside Signal you want back, select them for download. If they are still visible in Signal they should "download" from your local database to your pictures(or whatever Apple calls it) folder. Videos will"download" to Movies (or whatever Apple calls it_ assuming you had them set to download into Signal by default or had ever played them. I am assuming here that iOS doesn't also block downloading photos and videos into the phone from Signal. If it does, see below:
In a real pinch, chats could be "saved" by bringing them up one screen at a time and photographing them on an unlocked phone or a real camera. This works entirely without regard for any locking down-and is one reason you should never assume Signal can keep one malicious party in a group chat from saving everything. If they can't screenshot it they can still photograph it, and that might look like shit but it will be readable.
Photos it would be difficult to get enough quality this way and videos even worse, but might be better than nothing. I am assuming paid software is all the way off the table as it is for me.
If you can't jailbreak the phone well enough to allow exporting your data, I would advise an immediate end to the use of it for taking photos or using chat apps for anything you care about saving on grounds of it being "write-only memory."