Since they are old, i would imagine the power efficiency isn't the best on them for a 24/7 HA cluster at home. Unless you have an abundance of solar power or something. So I would use them as a test branch for whatever I want to do for self-hosting and learning
I would use them as learning platform for myself. Play with Active Directory DCs, replicataion, failover, recovery, networking etc. Just because more practice in that is what would be needed for advancement at work.
Others mentioned Kubernetes and Proxmox clustering. I could also use some sacrificial storage and compute to play around with those technologies so I could improve my self-hosted services.
Phone payments seem to be the main topic, which I never missed over the 10 or so years on LOS. Not /e/, but similar limitations apply.
Am I wrong for considering credit cards the phone for nfc payment an "all eggs in one basket" approach?
If the phone dies and you don't have your cards on you then you won't be making any payments until you gain access to your physical cards. That could be a problem in many situations nowdays.