What files from your Mac are you trying to sync to next cloud? If you have a Truenas already, why are you hosting files from your Mac instead of mapping a share directly from your Truenas into Nextcloud and working directly off of the source instead?

As for syncing photos from my phone to Nextcloud, I’ve had no issues over the past 3 years hosting it myself. I had one problem with a lot of conflicts where permissions on my truenas wouldn’t allow nextcloud to delete them, so I had a manual cleanup process last month but that’s the only problem I’ve had. I just switched to Truenas a few months ago from QNAP and am still learning the caveats of their very granular permissions but everything generally works about 99% of the time.

Any combo modem router is typically trash and you NEED separate modem because if you get a combo you will be in the same situation. They will flash the combo unit with the same firmware wether you own it or not.

You will want an aris modem from there approved list and a good wireless router. When you swap out your modem you will need to call in so they can flash it with thier firmware (which is fine). You can then configure your router as needed.

I can’t recommend a wireless router because I have a Unifi household and have been out of the consumer space for a while. I hear netgear nighthawk are still creame of the crop though.