And ads definitely show up in YouTube and such.
If what FB is saying is true then the move by Apple helps Google. There's more or less two options for online advertising. So if companies spend less on FB then they're probably going to spend those dollars with Google
https://apps.apple.com/us/app/google/id284815942
Google search, in an iOS app. Not everyone uses it, sure, but has over 341k reviews. Facebook, as a point of comparison, only has about 4x more reviews at 1.2M. 4x is a lot, but it's also a lot less than I'd expect over something primarily used in the browser.
Click on the dev's name and it shows everything that dev has published.
Google has 17 apps for Apple devices.
https://apps.apple.com/us/app/google-one/id1451784328
https://apps.apple.com/us/app/screenwise-meter/id1455562397
https://apps.apple.com/us/app/google/id284815942
https://apps.apple.com/us/app/notable-women-ar/id1425071635
https://apps.apple.com/us/app/just-a-line-draw-in-ar/id13672...
https://apps.apple.com/us/app/google-tasks-get-things-done/i...
https://apps.apple.com/us/app/looker-mobile/id1533498070
https://apps.apple.com/us/app/google-podcasts/id1398000105
https://apps.apple.com/us/app/google-stadia/id1471900213
https://apps.apple.com/us/app/google-fit-activity-tracker/id...
https://apps.apple.com/us/app/google-fi/id1413936031
https://apps.apple.com/us/app/grasshopper-learn-to-code/id13...
https://apps.apple.com/us/app/youtube-music/id1017492454
https://apps.apple.com/us/app/google-keep-notes-and-lists/id...
https://apps.apple.com/us/app/google-maps/id585027354
https://apps.apple.com/us/app/youtube-tv/id1193350206
https://apps.apple.com/us/app/youtube-kids/id936971630
https://apps.apple.com/us/app/youtube-watch-listen-stream/id...