Can you somehow automatically convert your 1.8.9 texture pack into a 1.16.5 texture pack in Minecraft?
I would use it in 1.16.5 without changing it because in newer versions there are only more blocks. I think they changed something with gold saws.
Some blocks and items have to be named differently in order to be changed.
Does it work completely without errors?
No idea. I have never used it before.