When the GDPR first came into effect, Oath/Tumblr initially offered the option to turn off "partner" access to your data. I did so, turning off each one in turn. (Of course, this only applies if you're signed in)
There were.. more than I'd anticipated.
299.
Here they are:
https://www.lapinity.com/text/net/Tumblr%20partners.txt
I don't visit Tumblr any more.