It’s boring. It works.

OwnCloud is written in Go but employs an open-core model. Some features are locked behind a proprietary paywall.

I'm running NextCloud, but I hesitate to call it good, because of its kitchen sink approach to features. I really want 2015 era OwnCloud with just files, it being PHP/MariaDB/Apache-based. I refuse to use anything that requires Docker, which is most of the slop alternatives currently available.

I'm not aware of any "Fix" besides whiping your install(s) and trying again. Try not to use a backup if you can, as it can keep the slowness/lag across installs.

It's really annoying.

I have maintained a Nextcloud server for a small business for the last 6 years. I agree when I started using it early 2020 that the ui felt less modern, but after some updates down the road up until now it looks completely like it is from this era. Am I missing something? However, I never complained about the UI neither then nor now.

I know it’s not the question you asked but I feel not enough people know about it as an option and it’s really as good as Google Photos.

SSDs shall be single sided and gonna need heatsinks, but I believe it works well and is not tied to any manufacturer for anything.

If you want go all-out get ASUSTOR's Ryzen based systems. You can use the stock firmware or disable it without wiping it and deploy TrueNAS on it. It's a beast.

TrueNAS has containers and applications and VM support so you can run any service you want on it.