Ads like this really arent all that scumny my dude, i mean at least IMO lol.

You gotta pay the creator to use the app. Sync isnt free, You either pay with ads, or you pay with your buckaroos. Thats just how it works. And its pretty transparent. No trying to dupe you, hes not secretly selling your data (at least as far as i know). Either view ads so he gets paid, or pay him directly. I dont see anything wrong with this business model. The issue i have with ads is the intrusiveness of them, or the stealth of them. Reddits ads are scummy because they look like reddit posts, thats not cool.

Implementing ads after getting a user base (like in your lemmy.world example) is different because they are changing the model. If i were to join an instance that started off with ads, id be less miffed because if i like it enough i can stay and view ads / pay, or i would move to a different instance. I wouldnt call it scummy. I would understand that they gotta pay bills to keep that server on, and thats how they decided to do it.

For what its worth, i am a FOSS guy all the way, and take all opportunity to block ads. But im also willing to pay for software that i think deserves it. I donate to my lemmy instance, and have paid for Sync Ultra, because they are both great and the maintainers deserve to get paid :)