What app am I allowed to use to screen record on iOS? Also, how can i show a timer while screen recording?

It's probably easiest to use the built-in screen recorder, as that's simple and captures audio as well. You can't show an additional timer without editing the video (on a computer).

Apowermirror

https://www.apowersoft.com/phone-mirror 1.52MB

Run the exe file install it etc.

IOS same application apowermirror

Make sure your IOS device is on the same Wifi network as your PC (PC can be connected via LAN)

now you can buy it ... or (cough cough) another way.. to get rid of the watermark