I had android 13 on S5, I wont say it was smooth, but it was more than usable. I replaced it mostly because 2GB off RAM was starting to get on my nerves. I couldn’t have more than 2 apps open without it putting to sleep the previous one. Multitasking was not very good on such a old phone.

I cant imagine what could be wrong on 3 year old phone. If it is not broken just install LineageOS on it and you should be good to go.