Can ball pythons safely climb branches thinner then them?

[Malum Argenteum]

I am not doing it for easier cleaning but because it looks much better than a boring sterile tank.

I would call the methodology you're looking for "naturalistic" -- wood rather than plastic, substrate rather than carpet, and so on. There are good reasons to aim for a naturalistic enclosure (or naturalistic elements): they look "better" to us, but much more importantly many animals seem to prefer natural materials over plastic. I give all my snakes both a plastic hide and a cork hide, and across taxa they consistently prefer to be both under and on top of the cork even when the positions of the two are switched in the enclosure.

There's also a case to be made for the "sustainability" of natural products over plastic, though not a case that can outweigh husbandry considerations. If plastic is better for the animal, then plastic is the way to go, full stop.

"Bioactive" is useful for (and was originally developed for) those animals that simply won't tolerate an enclosure cleaning, and that make waste products that are actually sort of amenable to processing by microfauna -- dart frogs and micro geckos, and that's about it. For virtually all other species, "bioactive" enclosures not only don't function as designed, but also involve expenditures of time and money that are better spent on aspects of animal care that actually benefit the animal in specifiable ways.

Springtails and most isopod species will not clean elevated wood branches unless the enclosure is at nearly 100% humidity, and even then not so much. Even in dart frog vivaria, the amount of spraying/scrubbing off of plant leaves to remove poop and algae is considerable.