For me it’s Whatsapp. Like 99% of people i know use it so yeh… i still need it. I am considering moving the Whatsapp Gdrive backup to a local backup btw.
Google photos is also a major problem for us. We have a lot of stuff that want to migrate to different service (or store locally).
Next cloud has done much of the heavy lifting. You can adjust android (if you’re stuck on android) to move photos, backup, contacts, and calendar to it using the next cloud suite of apps. Calendar and contacts can sync with it using davx5. I bought 5tb for $15 with hetzners managed next cloud service and i dont even have to manage it really.
I use proton for email and have use email aliases with my own domain pointed at my proton email, so that if i ever want to stop using proton I can easily migrate. I have my gmails in maintenance mode - when i get a new email for something I forgot I go to that website and either change the email or kill the account by asking for GDPR deletion. Even if you aren’t European asking a site for GDPR deletion will usually get them to comply because they aren’t going to go through the effort to check if you’ve moved or something.
And for YouTube I use freetube / invidious For music I use deezer, but ive also heard good things about qobuz.
WhatsApp wad a sticking point for me too in Europe. My landlord sends me my bills through it and every business uses it for appointments and customer service. I use a matrix bridge to give me an extra layer between it and my devices, which helps so i dont have to have tbe app itself.