Gmail is an email service. Like the fediverse, email is federated.
By changing your email provider, do you really lose anything? You can still contact your friends, contacts and even various customer suports. You also can recieve emails from popular social media apps. If you degoogle from atleast one Google app, maybe Gmail could be the easiest and least life changing one.
While, Youtube could easilly be one of the most difficult to degoogle from. Not like literally but emotionally. Like deep down you know you can find mostly all you might need on something like Peertube but not all the entertainment media like on Youtube. You will also become a social outcast if peertube is the only app you use. You might not understand channels people mention in day to day talk from youtube or references.
If you use exclusively fediverse apps and sites, Chrome could be almost just as easy to replace as gmail, longterm. However If you use Youtube it won’t surprise me that Youtube downgrades your performance and user experience in what ever means neccesary on competing browsers.
Google Photos is the one i am having biggest problems replacing
Store i can store my images anywhere, but nowhere can I type in the search files “Italy” and see all the images I took in Italy, or “John” and see all the images I have of people called John. Or even just search for “car” and show all images of cars.
I get much more out of my images using that service than any other image storing option i have tried
Check out immich. Not there yet but its getting there.
There’s probably no alternative as polished as that, but it’s not too far off either. You can kinda search like that with photofield (disclaimer: I made it), but many other foss photo libraries also support semantic search by now, LibrePhotos for one.