Are we not free to decide which software we use? If so, then your question can only be answered individually.

Your second question confuses me a little. There is nothing inherently pro or anti capitalist about the tech, especially in light of the first point.

It’s worth twenty dollars to not see ads that don’t exist in the first place?

To me, yes. I spent a decade on sync pro for reddit, so it wasn't even a thought. Others don't have to feel the same way or use it.

It’s worth introducing capitalism to the fediverse?

I like the dev. I like supporting the dev to continue improving an app I like.

Value is subjective, but I do consider worth it to fund LJ's work on the app.
He has been working on Sync for years full time, which is why Sync was/is one of the most polished and frequently updated apps out there. If there's a small price to pay for it, so be it, the guy has to eat.

So developers shouldn’t be allowed to make money for the time and effort they put in to making apps?

As a developer myself, yes. There's nothing wrong with a dev of an awesome app to make some bucks, and no, it's not the same as reddit, you know who gets the ad money there, here is straight to the guy developing the app. If I don't feel like paying, I can always move to another app.

It's worth twenty dollars for a better experience with more polish than any other app. No question.

Schrödinger’s Ads

Easily

I don't think a person selling an app is capitalism. There's no means of production, there's no apparent attempt to appropriate and profit from stuff that rightly belongs to the people who actually made it. Unless Sync is actually written by a bunch of people who are not getting ownership of the project?