No to "flash firmware via CLI" or to both that and "flash firmware TWRP"?
If no to both, what approach do you recommend instead?
My phone is not rooted btw (never found it necessary for daily use). I can't really find clear guides online, everyone seems to have different convictions on the matter, and that's not reassuring.
Update: I'm on TWRP
3.3.1-0now, which is the latest version willing to boot on my device. Unless a higher version should work, I guess we can leave it at that. This leaves the Firmware question.