not a final solution but… so far… after some research… I would forget the default type files and go with
- a custom panel field ( [My first Panel field | Kirby CMS (getkirby.com)]
(My first Panel field | Kirby CMS) - get inspiration from How to upload an Image while creating a Page in a Section Plugin - Plugins / Kirby 3 plugin - Kirby (getkirby.com) (thank you @dennisb…)
- more info with Uploads | Kirby CMS (getkirby.com) and maybe define a custom route for upload…
Hope it helps others