Blocking ads on YT is very hard because Google uses encryption and randomly generated hosts to serve the ads. Therefore, it’s much easier to block ads within a YouTube app than with an external tool (like Blokada). NewPipe and YouTube Vanced are featureful, great alternatives to the official YouTube application; please check which fits better for you.
Since some time there is a new list, maintained by Jerryn70, with the purpose to block ads on YouTube. There are mixed reports on its effectiveness, so our recommendation is to try it yourself and see if it works for you. To enable it in Blokada go to Ad blocking / Host lists and select ‘YouTube Ad Blocker by Jerryn70’. Else you can use one of the alternative clients mentioned above.