I tried Nextcloud a while back and was not impressed - I had issues withe the speed of the Windows sync that were determined to be "normal" with no roadmap to getting fixed. I'm now planning to move off Windows desktop so that won't be an issue - so I thought I'd try again.
I went to nextcloud.com, clicked on Download-> Nextcloud server -> All-in-one -> Docker image - Setup AIO. This took me to the github README at Docker section. I'm already running docker for other things so I read the instructions, setup a new filesystem for my data directory and ran the suggested docker command with an appropriate "--env NEXTCLOUD_DATADIR=". I'm then left with a terminal running docker in the foreground - not a great way to run a background server but ok, I've been around for a while and can figure out how to make it autostart in the background ongoing. So I move on to the next step - open my browser at the appropriate URL and I'm presented with a simple page asking me to "Log in using your Nextcloud AIO passphrase:". I don't have a Nextcloud AIO passphrase and nothing I've read so far has mentioned it. When I search for it I get some results on how to reset it, but not much help. I could probably figure that out too, but after reading some more I found that Nextcloud requires a public hostname and can't work with a local name or IP address. I'm already running my home LAN with OpenVPN and access it from anywhere as "local" - I don't really want to create a new path into my home network just for Nextcloud.
I'm sorry - I know this sounds like a disgruntled rant and I guess it is. I just want to check that I'm not missing obvious things before I give up again. All I want is a simple file sync setup like onedrive but without the microsoft.
For just files I'd use Syncthing or Resilio (I keep hundreds of gigs synced with ST). Resilio has a feature that's very useful - Selective Sync. This allows you to setup a sync job that syncs the index of files, but doesn't sync the actual files until you select a file(s) to sync on the remote device. I use this to access my media files from anywhere (3TB) which I obviously don't want to try to sync the entire folder to my phone, etc.
But since you effectively are on the same LAN, you can use any file copy tool the respective OS's support.
Though for WAN connections, I prefer tools with some redundancy/resilience, since those connections can be slow or experience drops, and regular copy tools aren't designed to contend with that (in Windows the only tool I can think of off hand is Robocopy, but I think Teracopy will at least show you if a file copy fails).
It really depends on your use-case, what you're trying to solve for.