It won't change the format of those already in that format, but all new ones will be saved as .jpg. You could open each of the HEIC photos, choose save as copy and the copy will probably be saved as .jpg. If it does, you can then delete the HEIC photos--unless you want to keep them.
The same problem just started on my Galaxy s21 and it stymies friends I send pictures to. I've read the solutions you and others listed but can't find the specific location in Settings to change the heic setting! This is an S21 phone. Many thanks.
