i am not sure if its still a thing but there was an app that automated this method for spying on your contacts. it even became quiet popular in the different app-stores.
But all of that is very limited data. Imagine what Meta itself can do with all the collected metadata. I wonder where their name came from
for TB -> TB-flatpack simply pasting from ~/.thunderbird/ to
~/.var/app/org.mozilla.Thunderbird/.thunderbird/
did work for me. I might try betterbird sometime.
I got it on sale a couple of years ago. It is a very decent messenger. Although I use Signal most of the time, its nice to have Threema in my messenger collection as well :D
I always wonder how would that even work? Encryption is no mystery and openly available to anyone.