Are you familiar with https://web.whatsapp.com/ - i.e. through that site you can use WhatsApp from your computer’s browser instead of relying on your phone. Instructions here: https://faq.whatsapp.com/834124628020911/?cms_platform=web
You need your phone to authenticate against it; so it’s worth doing that whilst your phone’s working.
WhatsApp Web talks to your phone to authenticate you (i.e. I believe your phone and computer have to be on the same wifi, as well as having done the one off QR code piece mentioned above). However; you don’t need to use anything on your phone to authenticate; so don’t have to enter your pin; so even with the phone in its semi-broken state you can continue to use WhatsApp on your computer. Hopefully that’s helpful for if your phone hits this issue again (e.g. if updates aren’t disabled).
For Signal it looks like a similar solution’s available; though I barely use the phone app and have never used the desktop app, so can’t comment… Worth investigating if you rely on it though.
Hope that’s some use.