[ardy42]

> Why are there >3 rows of Fn keys ? Are they all different? Or Are they placed so to quickly access ?

It looks like the creator just used whatever random keycaps he had. There are also duplicate arrow keys and duplicates from the navigation cluster (e.g. pgdown). The katakana(?) keys also look like they might be incomplete.

[FreeFull]

I know that at least Linux does support additional F keys beyond F12, since there used to be computers/keyboards that had them. I'm not sure how having more than 255 keys works out, though, I haven't looked into how USB HID handles it.

[JdeBP]

There's enough for 65535 different usages in the keyboard page alone, and there are more available in the consumer and system pages. But nowhere near all of those have definitions.

There are defined usages for function keys up to F24, and for all of the dedicated function keys that one could find on Sun and IBM keyboards, such as Stop, Again, ExSel, and CrSel.

[mncharity]

https://github.com/torvalds/linux/blob/master/include/uapi/l...

[JdeBP]

Those are not USB HID usages, notice.