I said respect ratio, not overall size one compared to the other.
As long as either width or height is fixed but not the other one, the ratio is respected
Indeed usually when flags are together a standard size is used.
We just need someone with a little time and basic graphic skills to have missing ones
(otherwise maybe I'll do it if I have some spare time this week...)

Tönz was just here https://www.imcdb.org/vehicle.php?id=1703493
but I don't know if the e-mail connected to his forum account still works.

This account is still working, thanks for contacting directly. I just now did the missing flags in traditional style, I hope I haven't forgotten any country (some of them I haven't even heard of).

AH | Austria-Hungary

BL | Saint Barthélemy

CW | Curaçao

GG | Guernsey

IM | Isle of Man

JE | Jersey

LY | Libya

MO | Macau

ND | Northern Ireland

QC | Québec

RH | Rhodesia

SS | South Sudan

SX | Sint Marteen

XK | Kosovo

YU | Yugoslavia

Thanks! I'll put the old flags back then, I hope that now everyone will be mostly happy again

Macau was already in the list ("Macao SAR")

Two others that I added and forgot to mention:
RE (Réunion) https://en.wikipedia.org/wiki/Flag_of_R%C3%A9union not the French one, the other, though that unofficial, seems used
GF (French Guiana), it was in the other list I had, I don't know if it is needed but why not...

Not useful, because these flags, are regional flags, just like the Catalan flag, after if you want to add them all.
https://fr.wikipedia.org/wiki/Liste_des_drapeaux_des_r%C3%A9gions_et_territoires- _fran%C3%A7ais
By cons you can add the Kanak flag for New Caledonia because even if not recognized, it is used officially.
https://fr.wikipedia.org/wiki/Front_de_lib%C3%A9ration_nationale_kanak_et_social- iste#/media/Fichier:Flag_of_FLNKS.svg
https://fr.wikipedia.org/wiki/Nouvelle-Cal%C3%A9donie
Especially on municipal vehicles.
https://caledonie-ensemble.com/wp-content/uploads/2013/03/Police-municipale-canala.jpg
https://la1ere.francetvinfo.fr/image/WNCPUUkXWgPbnRCHCyeEdf4GZzE/930x620/filters- :format(webp)/outremer/2019/10/03/5d95d18f76ebb_garde_champetres_2-560919.jpg
https://scontent.fcdg4-1.fna.fbcdn.net/v/t1.18169-9/12096261_1153799801300998_74115206157179383_n.jpg?_nc_cat=104&ccb=1-7&_nc_sid=973b4a&_nc_ohc=kwIYRziYW28AX8GFlMR&_nc_ht=scontent.fcdg4-1.fna&oh=00_AT_8qqYwOadgYt_e1URjSguoygDyYU02aQgE3dh8b_voew&oe=6362B166

Maybe it would be easier not to add too many then

I think so too. We probably should limit our country selection to present souvereign states and past ones with a relevant, distinct or unique automotive sector.

Thanks antp! Now the Japanese flag looks normal again with it's slight outline, instead of just a red dot on a white background.