[watermelon59]

Not the person you're asking, also not an expert, just someone who enjoys lifting weights (Olympic style!) and has spent a lot of time around people whose livelihood revolves around fitness and strength sports.

Rounding your back is only an issue when loaded. You don't wanna round it when squatting or deadlifting (but the Barbell Medicine folks will tell you it's not that big of deal, most of the time). If you're just moving your body on its own, you should absolutely do things that involve rounding your back, like touching your toes. If your back wasn't meant to move that way, it probably wouldn't move that way... or at the very least your body would immediately give you warning signs to make you stop doing that (like when you try to bend a joint the wrong way).

[crashbunny]

I was doing some beginner gymnastics strength exercises. I saw an advanced video I and couldn't believe what I was seeing.

These advanced gymnasts stood on a box, bent down with straight legs touching their toes, grabbed onto barbell with light weights, keeping their legs straight, slowly stood up keeping the barbell close to their body.

The explanation was the back is designed to do that and if you don't it you lose the ability.

That's not something I would ever attempt, but goes to show if you know what you're doing and have the necessary foundation in strength and flexibility, round back is not only OK but necessary to keep range of motion and strength. Again, I would never attempt that myself.

[AriseAndPass]

Thanks for commenting! I hear what you're saying, but I think it's perfectly possible to injure your back with bodyweight exercises over time. Even if we're just talking about yoga, there's a good amount of evidence that incorrectly practiced yoga can and does cause back injuries over time.

Now I'm sure that the optimal answer to that would be to make sure you correctly practice yoga. But the back is probably the worst joint I can think of injuring, and at the same time I'm basically just watching youtube videos and copying them - which isn't really a guarantee of correct practice. So I try to err on the side of caution by keeping my spine neutral :)