Mike, I’m an iPhone 11 Pro Max owner as well (I bought the one with the biggest screen as I have trouble with small type). I tested HEIC stills against JPG stills. There was no quality difference. Hence converting the entire folder to 16-bit TIFF for processing (if quality is paramount) or 8-bit jpeg makes absolutely no difference: you lose nothing. iMazing has a very good converter and it’s free.
FYI, the licensing fees for HEIC for commercial software publishers are extortionate. You’ll see HEIC in free open source applications sooner as free open source software developers don’t have to pay the HEIC license fees at all (there are some hurdles for them to jump over as well to justify/limit their use of the code but some use is allowed).
Based on what I’ve seen from my iPhone 11 Pro photos, there’s no need to jump to TIFF for the conversion. The files are good but not amazing. These were finished in Photolab from jpeg conversions.
Don’t let Apple rain on your photo parade with promises they can’t keep: HEIC is only as good a container as the information you put into it. HEVC video is a bigger deal. Video files are so much larger and the continuous data rate matters. It’s the same nightmare for editing though – HEVC should be transcoded for editing on anything except an iPad Pro.