iCloud photos upload

I just downloaded all my phone pictures into my computer to release space in photos (iCloud Drive).

They all come down in iPhone-made picture format .HEIC (never seen that format before)

So now I'm trying to upload only a few most important pictures, but iCloud only supports .jpeg uploads.

Is this a joke?

Them coming down in .HEIC then not being able to come up the same way they came down?

What's the process here?

*Changing the name's file name to .jpeg gives upload file format error...

Any tips? Thank y'all!