Why is Wi-Fi randomly graying out/ loosing signal?

Hello there,

recently bought second-hand iPhone 7 with beat up case and cracked screen.

It has been updated to iOs 13.5 with fresh reset, and when trying to connect to Wi-fi it shows routers, and can be connected, but after a few seconds it drops connection, and hides all routers. After re-enabling it, it shows again - can be connected for few seconds - and drops connections. So for a while, till ‘settings‘ app glitches out and wi-fi toggle becomes ‘grayed-out‘, cannot be enabled. BT toggle is switchable but cannot find devices/ connect. But never ‘grays-out‘. Priveous owner says before update it was okey (doubt that, but ok, may be).

I tried ‘airplane mode‘, restart, restart network settings, but nothing.

BUT - after making hard-reset, till it goes to ‘Hello‘ screen, wi-fi toggle comes back and connections can be made - but as mentioned above - few times drops out - glitch - ‘grayed out‘. And so on, on loop.

Before screen comes and i try to open it up - it may be antena what is acting up, software issue or it is not fully separated wifi chip (gray one) what everyone suggests to reball or fix pads?

If latter, i shall sell it, as I have not got equipment to do the job - but as I searched - for this toggle is always peramentaly ‘grayed out‘. So there may be hope.

Any suggestions?

Thanks.