I'm sorry but what?

You have been lifting weights somewhat regularly for 25 years, majority 3x8-12, and the switch to 5x5 increased your dumb bell bench press from ~20kg to ~35kg?

There is just no way. That is extremely light weight. Like, most beginners who follow any sort of progressive overloading system will be at that level in 4 weeks starting from essentially 0

Just jumping in here to feed my ego :D

after 15 years of lifting, I'm currently pushing 4x10 with 50kg dumbbells on the bench. So yeah, 35kg after 25 years seems odd unless those 25 years weren't exactly "serious" or "consistent" let's say.

No judgment, but yeah