Hello,I also have 3 Macbook Pro 9,1 mid 2012 but my bluetooth ID is 05ac:821a instead od 821d, can't explain why.
I too felt that BT was working with kernels 5.10 and 6.1 but doesn't work with 6.4.
So I replicated the proceeding reported here and it started working, just as in the report.
