What @dagill2 said. Also, don’t conflate a regression in a lift with having lost muscle or progress. Skill at exercising the movement pattern is also part of the puzzle. My point being, you could retain all your muscle and potentially gain some and still see your bench press go down simply because you’ve lost some skill in the motor pattern. But keep training your triceps and chest.
Here’s an idea:
Single-arm DB floor-press.
Progression: