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?
If you can run EXE filles on your work PC and you just don’t have administrator rights to install software, you should be able to download a portable version of your favorite browser.
I used portable Firefox, Chrome, Notepad++, Eclipse, Sysinternals stuff and many more without problems that way.
Disclaimer: Althought this probably works technically, it might still violate some company policy.
It also works with Amazon FireTV (Stick) or any other Android TV box / stick, just in case you have already one lying around. ;)