Hi Eva, I moved your post to a new one, as the other post was related to specific issues on FP2s still running Android 7, what is not the case for you.
You write you have no SIM installed, do you mean SD or really SIM?
There are several possible reasons for reboots, beginning with simple things like a loose battery.
You say its since a few weeks. Did anything special happen? Have you done an update to the system?
You can try to run in dic:safemode to see if it is an app.
When you have a SIM installed how old is it?
What exactly means touchscreen not working? Does it just need more time to react and settle after the reboot? What do you do when this happens?
When you make a call and the loudspeaker turns on, will the screen go black during the call?