The market will definitely speak on this one since the platform itself isn’t monetized and there are tons of other options for those who don’t want to pay that much. If it ends up not being workable, it won’t be workable, and the model will need to adapt or fold.

I’d never pay that much for a phone app, personally, especially on android, because I’ve had apps that change dramatically to the point I no longer like/can use them. It’s a bit better on iOS because the devices are supported a lot longer with OS updates (literally the reason I switched after a lifetime with android flexibility - sick of apps not working and my phones not being supported officially for more than 2 years).

This isn’t to say I won’t pay for things I want and support - I did pay for a Plex lifetime subscription like 9 years ago ($100, it’s 120 now, and a large amount of paying for it is app access, but also managed home users so my close friends/family can be logged in to my account directly without impacting me in any way) because the value was well worth it after subscribing month to month to test it and using the free version for several years prior. The value for what I paid has increased substantially with new features and just simple longevity. The model seems to work well enough for what they provide, both to them and to their users. I can swap to another self-host if it falls apart, but in the 12 or so years I’ve been using it, only a small number of changes have negatively impacted me, and only slightly (tho I paid early, so if features were paywalled after being free, I’m not aware of it, tho they have made some previously paid things free, like plexamp). I can skip server updates and roll them back easily if it stops working with my OS, and my users wouldn’t know the difference for a long time.

This tends not to be the case with mobile apps because devices are constantly changing, and side-loading apks can be a challenge for your average person. It’s a lot less static overall than pc hardware, so app-breaking updates on older mobile hardware are way way more likely. I can’t afford new phones all the time, so that’s a problem to me.

I’m looking at the relative useful lifecycle of the software. If I can get maybe a couple years before my OS version isn’t properly supported to run the app anymore, and it’s difficult to fix without upgrading hardware or rooting and flashing (not something everyone can or wants to do), I probably don’t want it. I turned off automatic app updates for years because of this issue, but they stop working after a while anyway.

I was talking about servers, not client apps.

Regarding the app, yes, $20 is too expensive for just turning off ads. Moon Reader Pro asks $8 for an ad-free experience, and yet I think it's a bit too much for me. But it's a market, and demand will correct the price. If nobody pays $20 to disable ads, the devs can consider reducing the price, at least temporarily. So I don't see any problems here.

As for totally free apps, I consider them as a sort of gift. Some people are giving away the results of their labor for free, maybe because it's their hobby, or because of ideology, but definitely because they have spare time to work on their apps. But it can change, and active development can stop. The only thing able to motivate them to continue the work is a profit, allowing them to spend some time without sacrificing anything else. We can end up with ads, subscriptions, single-time payments, or maybe just donations. I think it's inevitable for active projects.