Thanks for your attention and advise, I'll stay on what works, even without security updates.🤗
Don't have in mind to destroy my hardware, which lasted so long, for a false firmware.
When times come to change, I'll start again, as all of us, at zero and format my mediums to this damned APFC.
I've done this about 50ish times, and never has a convert to APFS ever worked for me. I always have to convert to APFS, then run the full installer, THEN the patcher to install the patches. This will do an in-place upgrade which will preserve your files and settings. In all the times I've done it, I have never lost any data, just the time needed to run through the full installer.