Got a few old iMacs here (10 years+) and they run with newer Mac OS versions, but they don't run well. Upgrading iMacs is a pain as well and since the ones I go

Got a few old iMacs here (10 years+) and they run with newer Mac OS versions, but they don't run well. Upgrading iMacs is a pain as well and since the ones I got have only 4G Ram it kind of hurts using them this way. I was given the task to get a "modern", "minimal" System up on it for non technical users. Windows 7 ran ok on them, old Mac OS ran great Win 10 crashed/had audio bugs, FreeBSD somehow ended in a bppt loop and now I got a system running kde plasma on it and I have to hope that my client will find this acceptable as well. I would, but that's just me.