Tailscale offers a paid Mullvad integration, where you can select most Mullvad servers as exit nodes. Works quite well.

Would you mind sharing the code?

Revolut works fine on CalyxOS.

Revolut still works well on CalyxOS.

I use 4 different European banking apps without issues on CalyxOS.

Hi OP, I am in a similar situation as you were so I wonder which solution you chose at the end and if you are happy with it?

CalyxOS still provides extended support for Pixel 4a until August 2024.

That’s already possible either by using a custom ROM or by connecting to a PC and using adb.