I’ve used both self-hosted Nextcloud, and an instance set up by my school. I have the client on two different Windows machines, and I can confirm the update either tries to kill explorer.exe, which doesn’t work half of the time, or forces a restart, so you’re not alone with this issue! I also hate the client UI and how it displays conflicted files when multiple people are accessing the same folder. The whole file sync thing feels like a poor attempt to copy Dropbox. My school discontinued Nextcloud support last year because hosting/maintenance took too many resources, they switched to Microsoft i.e. OneDrive and it works much better.