Why, yes, I am flying with an IBM Model M2 keyboard and a handbuilt PS2-USB converter for it in my carryon. Doesn't everyone? 😉
https://mastodon.social/media/LSs9PtF7X6EESMvnoHo https://mastodon.social/media/ZqnjJCUjkU0dcFoxJAg
(credit where credit due: converter running TMK firmware, with keymap modified to turn Caps Lock into "Windows" key. I just modified the keymap, compiled it, and soldered the thing together.)
Late late follow-up: looks like it was some kind of USB 3 compatibility thing, based on the strange dmesg output I searched. Not sure if re enumeration due to Caterina bootloader is the cause, or if the keyboard boot hid descriptor is the confusion (since I guess it's a bit unorthodox by design), or what...
There are more weird USB compatibility issues out there than I had realized.