I was in a similar spot and gave up before starting. This is due to several reasons: 1) My circle of relatives and friends, like yours, neglect their privacy and would not engage with me in a serious conversation regarding it; 2) educational institutions, businesses, organisations and even governmental bodies may rely on WhatsApp for communications; and 3) the two big telecom monopolies offer enticing mobile data deals for using WhatsApp.
While I am not saying you should give up, you should go for modest goals (e.g. converting your close family to signal when chatting together) and eliminate optimistic expectations so you don’t get crushed.
You can still freely access the playlists on https://open.spotify.com/ without an account. And Newpipe has a share function for local playlists. You won’t be missing on a lot, just don’t fall for the consumerist trap and break the social boundaries.
Edit: You can also access banking services from their respective website. Don’t give them power over you by downloading their apps.
Izzy removes packages that are mutual with F-droid after a week or so. See here.
And apkgrabber not getting updates isn’t crucial if it the app works fine as it is intended.
Yes they are clean APKs, i.e. not modified and the original signature is preserved. So they’re as safe as the Google Play Store.
Regarding updates, I recommend checking out https://apt.izzysoft.de/fdroid/index/apk/de.apkgrabber
So for how long could they have been doing it?