Confused about training to failure and frequency, what would you do?

Hey guys,

I’m currently training upper body only due to an injury (no chest/legs for now). My routine is basically back, shoulders, arms, traps, forearms, and core (no pressing movements). I usually train most sets close to or at failure.

My question is

Is 3 days/week enough if I’m training hard?
Or is 4 days/week better for growth even with failure training?

Also, is going to failure on most sets actually productive or just hurting recovery?

I’m around ~28% body fat (71kg skinny fat)and my goal is to build as much muscle as possible while I can still train around the injury.

Would appreciate any practical advice - thank you!