Since I updated my FP2 to Android 9 (Fairphone OS 21.08.1-rel.0) a couple of months ago, some apps crash regularly. Telegram and Instagram seem to be affected most, but also the camera app and other apps. The apps just freeze and the only way to fix it is to force stop them from the within Apps and Notifications settings and then restarting them.
Telegram sometimes crashes every minute or so, making it impossible to have a conversation on that platform.
clear the cache oft the Apps, by holding the app pressed, click in the little “i” , select storage and clear cache. Probably also clear storage (this normally does not delete e.g. pictures, but e.g. password and user name etc)
for Instagramm you could use the browser instead of the app, and just put a link on the home screen
for pictures you could use another app, like e.g Open Camera
I have also experiences problems, which I documented on two other threads (replies to threads by other users; you can also read the experiences of the other users):
Nothing “fixed” it for me, but some changes may improve your experience. Nowadays, I only have some temporary crashes with Signal (which is the app I use the most with my email client and the browser).