Xiao Mi doesn't even try to hide it. They'll send your entire gallery up, make you accept their borderline insane T&C's just to use mundane apps (file explorer comes to mind), etc. They will reset your default app associations with every update and don't even let you unlock the bootloader unless you wait up to three months in some cases - and you have to register with your personal information and IMEI in order to do it.
It's nonsense. I'm really close to getting a "dumb phone" and calling it quits for mobile.
"Uploading the entire gallery" is exactly what Google Photos and iCloud do. Samsung tried its hardest to get me to agree with it too. Even OneDrive tried to pull a fast one on me at some point. It's par for the course for modern operating systems.
I bought Xiaomi with the hope of it becoming popular enough to get LineageOS support, but a month after I bought my phone they released a slightly different version that actually became a hit so I was stuck with MIUI. The hardware in my phone was about equivalent with phones twice the price at the time and even features an IR blaster, which no other brands seem to do anymore, so it was worth a try.
If you read the T&C and deny the prompts, it's not that bad. You need to go through every Mi app's settings and disable ads, but after that you can use them just fine. They're great phones for the money if you're willing to deal with denying the stupid prompts. I very much knew what I was getting into, I just lost the LineageOS gamble. They come with Google Play so you can just download Google Drive/Photos/Files/Dialer/whatever and use the phone like any other.
I wouldn't recommend them to the average user, though they're often still a better deal than most of their competitors in terms of value per dollar.
Luckily, another custom ROM project picked up my phone and I'm pretty happy with it now. They're great phones for tech savvy people looking to save hundreds of dollars if you've got an hour or two to clean up the crap.
I'm no fan of the stock MIUI experience either, especially china-only variants, but with that said...
The bootloader unlock is 7 days and has been for every xiaomi phone I've owned.
You can turn off "Sync" which is xiaomi's backup/sync service if you don't want to sync stuff up to the cloud...
Providing your IMEI / phone number aka "personal info" is standard even across Apple with registering AC+ etc.
There's community roms that remove all the chinese bloatware that comes preinstalled (https://xiaomi.eu/community/) plus add a bunch of new features that make it a pretty awesome experience.
It's nonsense. I'm really close to getting a "dumb phone" and calling it quits for mobile.