I have a 10 year old laptop of very low specs. I had given a detailed description of the specs and made a post regarding the use to which it can be put, and more or less everyone pointed to self hosting.
Now, if the machine is powerful enough, why not put it to some productive use ??
And so l'm exploring an unknown territory.
From my experience, you can easily repurpose any old computer as long as it boot.
when i sort old computer. i divide them into three categories following the potential computer power.
put proxmox on it and discover the you are now a server admin ! Congratulations.
Replace the hdd by a ssd for more perceived speed.
Second Tier -> less than 6gb of ram -> it will be a bare metal server. Plenty of fun to have. You will restrict yourself to command line. No graphical UI (mouse and screen are not a necessity) Try to connect by ssh as a first challenge or try to do the linuxchallenge. Know that you will fail a lot, but when it work it will be very very rewarding. Put servers on it ! like adblock or anything from here -> https://selfh.st/
Last tier -> 2gb of ram or less. Very old computer, it is more of a heating element than a computer. Well it will be a router. Try to put opnsense or opnwrt and learn about networking. To add ethernets ports usb-ethernet adapter from tplink or other work well.
This tier list is from someone that have the luxury of owning multiples of thoses old computer, is quite passionate and work it the field. Your mileage may and will vary. Your need are your own, so try, fail, learn, experience, progress at your own rythm and succeed. Have fun and take care. Report if you have any success of some self-hosting lemmy board ;) You will be cheered upon and given passionate advice. Fail and post your failure and you will have the same reaction ;)