Bent in which way?
Rear triangle on a steel bike can be straightened out if you are careful.
Front triangle shouldn’t have issues unless it’s bad from the start. (that requires a table and skill)
Only bike I have straightened was a steel huffy (not worth working on)
It had a head tube that was twisted so wasn’t fixable… Rear was easy enough to align though.
Some of the things I replaced for fun
Some things I broke as I am learning to fix bikes (Hubs mainly… when a cog comes off unexpectedly it usually takes the threads with it)
Others just did wear out that fast… last chain only gave me around 1,000 mi but I rode in a lot of rain / mud and used an awful chain lube. (It was well over 1% out of spec and all winter I had a knocking in my pedal that I just couldn’t figure out)