Next thing I know is that Facebook started giving me ads for diabetics.
Having such an influential company know about your illnesses and sell that to advertisers or healthcare insurance agencies or credit agencies or god knows what else is frankly terrifying.
On the desktop website go to: Settings | Ads | Your Interests. There is a huge ontology of various subjects that have been algorithmically assigned to you. If you remove these, I believe ads targeted to those interests should go away. I periodically just sweep them all clean so I have no interests. I get very few ads and those that I go get are completely generic. I never see anything that would seem creepily aware of who I am.
What they sell is the ability to target you based on it. But the data never leaves FBs servers!
So if you remove the tags from your settings, advertisers won’t be able to target you with them anymore
You could argue this is the user’s own fault, but prior to Cambridge Analytica, there was very little public understanding of what “connecting” an app to Facebook really meant among the general population.
Also, just because Facebook doesn’t sell this data today does not mean they never will.
But Facebook issnt selling that access! Access to the APIs is free.
Now users just giving any random app access is a whole different can of worms...you have the same issue on Android and iOS with permission dialogs...people worry about Amazon Alexa recording everything they say, but will give any app microphone/camera access to do just the same if the app creator is ill intended.
It also gives you the ability to hide ads like that in the future
The advertisers don't get a list of the people that see their ads.
Which means it is likely that the Facebook algorithm is doing that without even prompted by the advertiser.
Did you visit a lot of links related to T2 diabetes? Another possibility is that the Facebook pixel could have helped the website target you again.