after installation through adb sideload, the installer(or twrp itself maybe?) indicates that i have to reboot recovery to install further zips, i do not boot the actual system, i boot to boatloader in order to boot the recovery again and install gapps.
So to answer 2), "before" since i never even had the chance to install gapps anyway, device is already completely bricked after flashing lineagos.
I will try to use your advice about the lineagos recovery. It might be that twrp completely ruins the paritioning when flashing android 11 on a android 9 device? Will know more soon.
Edit:
"In some cases slot b can be unpopulated or contain much older firmware than slot a, leading to various issues including a potential hard-brick. We can ensure none of that will happen by copying the contents of slot a to slot b. This step is NOT optional."
wiki.lineageos.org
*oh, hello, potential hard-brick? yes*
I guess for my future devices, i shouldn't just rely on "let's just boot TWRP and flash this image and everything should be fine"
=)
I didn't actually try these instructions, i simply let the stock rom update quite a lot and sideloaded it again and now things are not bricked, likely because now the stock rom is old enough to no longer cause these issue's again, hehehe.
There also aren't any documented cases of the issue I had anywhere on the internet because my case(buying a never opened/never used moto g7 plus off ebay, not updating the severely outdated stock rom and hoping twrp and sideload will work just fine) is rather... unique?