Yes its one time for android, if you’re earning money with ads or purchases, google will take 1/3 of that amount, then you will have to figure out taxes on your own and there’s also some special policies for selling online goods in India, but if you’re just making apps - its one time fee to be able to upload them to google play store, or you can just distribute with froid/github for free, which is a great route as well

From the perspective of FOSS developer:

I simply don’t want to pay €100 every single year to Tim Apple to make a free hobby app.

Android has more ways to distribute, and the “official” way is one time €25 fee and that’s it.