I just asked AI for confirmation.
Thai embassies know their online form doesn’t accept accents, hyphens, or cedillas.
Their own guide (the one you shared with me as an attachment) specifies that you should use the "international" English form of first and last names → meaning the version shown in the MRZ of your passport (the two lines with the chevrons <<<<<<). Visa rejections never happen for this reason, since Thai immigration is fully aware of this technical limitation.
If the form doesn’t accept a space or there’s a glitch, you can exceptionally write JEANFRANCOIS as one continuous string, but the most "official" version is the one matching your MRZ → JEAN FRANCOIS.
You must write it without accents, hyphens, or ç, exactly like in the MRZ.
The Thai form normally accepts spaces → so JEAN FRANCOIS.
If it rejects the space, just merge it → JEANFRANCOIS.
Thanks for your help! :)
Olivier