Literally any old PC is likely fine. It may be slow, it may struggle or even fail with some of the very complex software (perhaps you will encounter timeouts, or you will spend so much time waiting for memory to swap in or out to disk that it won’t be worth using) but you can run Linux itself on a potato and if your machine isn’t powerful enough, maybe you can get a second one and run different stuff on each, or just scale down your expectations and don’t try to self-host LITERALLY everything just because you can. Certain services are very intense, others will run on a very small piece of a potato.