I’ve been running Nextcloud on a 2014 refurbished thin client (Fujitsu business trade-in) with a 500Gb ssd and 8 gb of ram that I bought off our local equivalent of e-bay. The pc is very small, very quiet and runs Ubuntu Server (now 22.04). Nextcloud runs in a docker container with mariadb and redis. The whole setup typically uses around 25-30 watts, barely runs the CPU over 30%, ever, and does not run very hot.
So far in a year it’s been absolutely solid for me, the only hickup was completely down to me putting it behind a Traefik reverse proxy and forgetting to add the domain to the “trusted domains”
Overall file, agenda and task syncing is very fast and reliable, and for me has not missed a step. Actually I found file syncing far quicker than in iCloud so I have now switched iCloud syncing for most of my machines to Nextcloud as well, leaving 1 machine on iCloud to ensure Documents. Desktop and admin files can easily sync between iOS and macOS devices (the machine syncs Nextcloud into the documents, desktop and admin folders on my iCloud drive)
I sync all files to my Synology with their Cloudsync app, and back it up from there with Hyperbackup (encrypted) to my backup storage provider (Synology C2)
As an easy fallback I have a raspberry pi at my mother’s house attached to her cable modem with a 2TB external ssd attached, and I rsync my data there as well through a Tailscale connection. (where I live there’s no bandwidth cap)
I know the setup does require a bit of admin time from me (around 30 minutes per month), and a basic understanding of how Docker and Linux operate, but all in all if I’d have to choose again between paying 24,- per month (iCloud extra storage + Dropbox) and running my own I woud definitely do this again. My whole setup cost me around 300 Euros for the refurb and the ssd’s and I had the raspberry pi 2 lying around for syncing. So I reckon at the beginning of 2023 I’ve earned back my investment, and am very happy to be in full control of my data again.