I guess there is an option to activate to read DRM content (it exists on librewolf, not sure if it is there on Firefox too). it is activated ?

This is exactly what I did on my OP7 (only 4 years old). A new battery, a new USB port and a new back (thank you OnePlus for the back in glass).

I installed another ROM… And the only drawback on that “brand new” phone is that the camera is slow and not as good than the stock one ( even with Gcam or others derivative).