That sounds very much like the idea of SponsorBlock (but might need a bit of refinement to work for different ads of different length). You should definitely check out Piped for watching YouTube videos without any tracking/ads/dark patterns, I am very sure they will do something to remove server-side ads as well (hopefully).

And if it is just five seconds instead of 15, it would be way better!

HeLlOoOoO, wHaT nOw? It'S a Do Or DiE sItUaTiOn, HuRrY!

One reason this post gets downvoted might be that is violating rule 2 – no politicians.

And each version of Metafont gets an additional digit of e (currently at 2.71828182).

Piped. It uses SponsorBlock to also skip ads by the creator in the video, I am very sure they will update it to remove ads injected by YouTube as well. It is also very privacy-friendly.

Thank you very much!

Thank you so much for your suggestions! I guess I have to make an exception to my “free software only” policy when it comes to games (with the exception of Gamma). =D

Privacy is not the point of OP's question. A good answer would've been saying there is no WhatsApp client for Linux, and then (optionally) explaining that Signal has a desktop client and is a also privacy-respecting choice. Insulting OP by stating "You should not use this or that" is such a StackOverflow thing and helps nobody.

Edit: Just to make sure: I've never used WhatsApp and never will use it.