HEVC

On the iPhone the difference is negligible as the phone shoots a lower quality HEVC than it’s capable of. The only difference is space on the phone. I shoot HEVC. Why waste the space? Edit in HEVC and export to H.264.

I doubt you could tell the difference between the two.

HEVC creates smaller files, so that might be a factor on the phone. Minimize the space used and get the same result exporting to H.264.

> Would you also recommend that

I'd shoot HEVC and upload that to Youtube etc. If some of my often used upload site does not accept HEVC or .heic, then I'd shoot H.264 or .jpg.

> YouTube does support HEVC, but it is recommended by them to use H.264. Does it even make sense to shoot in HEVC for Travel Vlogs

AFAIK common users do not have much control how YouTube or Facebook re-encode uploaded files. So one FB recommendation was to upload max 2048 resolution image files with the best quality compression. I have somewhat followed that recommendation with my original images and also with movies (...hmm is there a max movie resolution in YT or FB for common user uploads? Just a few days ago I had to use ffmpeg to lower WhatsApp upload movie quality to make it fit to the 16 MB limit; IMHO the quality was quite good even after that...).

...sometimes I scale low-res images to 2048 to FB if I want others to see the "best" resolution without zooming in, although then it is later difficult to see which downloaded FB image really is the "best original available".

HEVC is capable of recording 10-bit 4:2:2 video. It’s a larger file and processor intensive. Apple choose a simpler format.

No. SDR can also be 10-bit. The bit depth has nothing to do with dynamic range.