Does this have NKRO and works with PS2 adapter ?
I think shark covered this in his article about it. If I remember right, the matrix was optimized, so it has closer to 6KRO now. It is not NKRO though.
It can support up to 10 simultaneous key presses without blocking, but this prototype and its pre-production code doesn't have phantom key detection fully working yet. Thus, I'm considering this an experience equivalent to and as reliable as 6KRO right now (lacking a more specific description). Of note though, the problematic combinations I found were subsequently tested by Unicomp on their latest firmware and they confirmed that phantom keys were no longer generating for them. So, the final product may in fact be stable at a higher key count.
I don't have a passive PS/2 adapter handy to confirm if it supports PS/2 output, but given they haven't told or advertised that capability, I assume no. But, if you meant whether it supports PS/2 to deliver 6KRO+, then there's no need. TO my understanding, USB not supporting more than 6KRO is a common myth or at least "artificial" limitation, enforced by the fact a lot of firmware writers only implement HID boot protocol that allows for just 6-scancode transmission for 'BIOS compatibility' reasons. NKRO with HID is very much a possibility, as demonstrated by Soarer's Converter and QMK (among others) supporting it or allowing you to force NKRO support. I'm happy to report that the Mini M indeed can send more than 6 scancodes, but the phantom key issue on my sample makes using combinations above 6 frustrating at the moment.
With it being USB and a new board from 2021 I would hope it's more than the original 2KRO, however, I think it still may be 2KRO due to the buckling spring. No need for PS2 adapter: it's USB. Unless you mean USB to a PS2 connector then likely?
Wonder if these LED covers would fit still? https://www.pckeyboard.com/page/product/LED
Indeed, it's much reliably higher than 2KRO.
Those LED covers would not fit. They're different dimensions. Although, I see no reason you couldn't cut the blanking plate down to the right size?