I find (for me personally) that I gain upper body strength so slowly and lose it so rapidly. The strongest I have ever been in my upper body was when I was practicing ashtanga yoga every single day. But really ashtanga yoga is just a lot of “super push ups” each morning when I wake up, but more fun.
I’ve also found that weight-based training works better for me than bodyweight, probably because I’m too weak to do full bodyweight much of the time. So bench pressing I progress faster than push ups if I’m only doing 2x per week.
This is anecdotal not science.