Linux Mint cinnamon is gold standard for quality IMO. All my modern systems that can comfortably run it do.
That said it also uses more resources than your old craptop may like depending on just how old we are talking about.
If cinammon is a little slow, try mint xfce. Its a lot lighter on system resources. Last time i tried xfce it was a great performance compromise if a little unpolished in places.
If Mint xfce is also too slow you can give MX Linux a whirl. Its way faster and more minimal that mint out of the box. Yet it feels modern and allows you to install all the same programs as mint from the default software repo including flatpaks. MX fluxbox is probably as minimal as you would want to get. Try their flagship xfce first.
If you are trying to beat new life into a 25 year old dying dinosaur Puppy Linux will do it, but you won’t enjoy using it.