Thanks a lot, it just did not came to my mind to try a 2230 M.2, since MikroTik did not provide a mounting hole for that.
But then i had the idea to use a 3d-printed 2230-to-2242-M.2 extender [1], which is a better-than-nothing solution, tbh.
I did now order a 2230 M.2 (Kioxia KBG40ZNS256G).
Will report back here, if i can confirm that this particular M.2 works with the M33G, so other users have something they could relay on.
@MikroTik
Please consider adding an additional mounting hole for 2230 M.2 to your products, since there is almost no market for M-Key 2242 M.2.
Except for the extreme expensive Intel Optane there is no M-Key 2242 M.2.
2230 M.2 are more available, since there seems to be way more demand for the smallest possible form factor than for the 2nd smallest.
[1]
https://www.thingiverse.com/thing:3996981