How to turn off "HEIC" feature in Photos ? Referred answer not working

I followed a previous chain on how to convert photos taken with the space saving feature of HEIC can be turned off. This is a nightmare for any artist or photographer; all of my art submissions MUST be jpg or cannot be submitted or accepted. I need a solid resolution. I tried the previous remedy advised switching to Compatible in Settings and Exporting and then Reimporting as jpg but this does NOT work. Please advise how to solve, this is a serious issue for any artists or photographers needing this not to be compressed to find an easy work around. This should have been an option you could do as an optional feature not just done for us all without our permission or notice. Thank you in advance!