According to Lilygo:
''The firmware version you ordered has no function for the middle button
You need to enter the configuration and directly search for the hotspot of SoftRF-XXXXXX on your phone after powering on. The password is 12345678
https://github.com/lyusupov/SoftRF/wiki/Prime-Edition-MkII
https://github.com/lyusupov/SoftRF/wiki/Prime-Edition-MkII.-Quick-start
Please refer to the guidance.''
I must also say that their reaction was very quick. Well done!
On the other hand, I installed Meshtastic and now the middle button works. So everything is normal ...