On mobile you could also have a look at NewPipe. It does not have automated downloads but it shows you a simple list of all the videos from your subscriptions without any algorithm-based recommendations. It shows no ads and is fully open source.

Also supports plenty of services other than YouTube.

Sorry, you’re right. It’s been so long that I’ve installed the app and always went via system settings that I’ve incorrectly assumed it was native.

— incorrect statement removed

Can you reach the server’s IP in general from other PCs in your network? Or is the issue restricted to the nextcloud service?