i haven't had a detailed look but i did get facebook and google takeouts (not in gdpr nation,so fucking close to one though)
facebook was from years ago and only had low-moderate usage, and even without giving fake information it listed very inaccurate interests:
>some south american football team
>iFunny.com
>Facebook
>Torque (physics)
>Steve Jobs
some make a bit of sense but are outdated or misinterpreted. others are literally retarded. i guess you need high usage for any kind of reliability.
of course now my account is filled with bullshit by me coming back once a month to like stupid minion quotes and angican christian pages from france and putting fake bio like being an tumblr otherkin married to a fake cousin i invented. i'll request another takeout to see how well this (allegedly) worked.
~500MB total download, 8MB when omiting messages
google had more alarming things simply because of how much i used to used it (used to Chrome+stock android, think of things like dictionary autocomplete suggestions), even with many or all privacy settings enabled.
there's clearly stuff they don't share (eg demographics/ad interests), i could only find a list of ads interacted with
do you think someone could just change their location to germany, use VPN for a few months and then successfully request GDPR/etc. deletion without them making you prove your citizenship???