Tested on a misskey instance.
I got the 422 error on Qoto when uploading the file, while I can update HEIC files to misskey.
However, my browser (both my phone and my laptop) doesn't support this format. And cannot display it properly.
And to make things worse, I don't know how to disable this HEIC thing in Samsung's confusing OneUI.
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I did a quick sanity check on Threema, and it seems like it will decompress.convert HEIC file into regular jpg/png file before sending to other clients.
The original file is 4.5MB in HEIC, but the client got 18MB of file. Clearly it's got decompressed. Also tried the normal JPG format. It takes 4.6MB instead of 4.5MB. I don't think I really care that 0.1MB per photo.
