Check your blocklist and keep in mind that YouTube is testing server side ads muxed into the media streams, which will not be blocked by traditional adblocking techniques.

If you can not install anything, your only choice is probably to set up a pihole or something similar on your network.

Edit: Some models seem to have advanced settings, where you can change the DNS - you could try to use adguard dns servers, or any DNS adblocker you want to use.