Hi there, thanks for sharing your experience. It turned out that exactly your solution also worked for me.
So I originally bought my i5 mini with 8GB RAM directly from Apple and upgraded to 16GB Ram (Crucial) myself. Everything worked fine as long as I sticked to Mojave or Catalina. When attempting to update to Big Sur, I had the BAG MAGIC error - I tried installing Big Sur any possible way (but kept my fingers off the revive procedure).
Until I read your comment, I did not consider returning to the original RAM sticks because some other user reported it not to be successful. Anyway, I just gave it a shot this morning because all apple service centres are closed for at least two more weeks (lockdown). Now I am writing this comment from macOS 11.1. Thank you.
I'll re-install the 16GB stick to have my increased memory back, but still curious to know If future security updates are affected. Will update if I run into issues again.