Welcome to the Make community!
The equivalent to a memory key in Make, is a Data Store.
For more information, see:
I have successfully implemented the data store as memory key for AI threads in many occasions.
Hope this helps! Let me know if there are any further questions or issues.
Note: I see hundreds of posts, notifications, and messages daily on this forum, so if I missed your reply, please message me to look at your reply.
— @samliew
P.S.: Did you know, the concepts of about 70% of questions asked on this forum are already covered in the Make Academy. Investing some effort into it will save you lots of time and frustration using Make later!