Google has news on what you will need to do for still being able to sideload apps:

* enable developer options
* confirm that you are not tricked
* restart phone and re-authenticate
* wait one day
* confirm with biometrics that you know what you are doing
* decide if you only want unrestricted installs for 1 week or forever
* confirm that you accept the risks
* enjoy the few apps that still have developers motivated to develop for a user-base willing to put up with this

https://goo.gle/advance-flow

They even have a video up where they try to make this all sound nice and positive:

@grote ok, what's freaking funny is this act is required UPON TURNING ON DEVELOPER MODE. Imagine if you need to do this every time you need to turn off developer mode because some banking apps check for developer mode. THIS IS HORRIBLE.

If you want to limit app installation, don't limit developer mode. Adb is borderline not ok but still, something else. Maybe this is only required if you need to enable app install from untrusted sources apk.