I managed after a call to the SEN hotline to get an answer.
Yes, it is possible to book those flights, now oprerated by Cirrus Airlines.
How: Look up the original Cirrus Airlines flight number for the flight of you choice. NOT the LH.... number, that one is useless.

Call the M&M hotline (Basic, FTL, SEN or HON9 and give them the exact flight details. Then one can book a reward ticket.
Request: Can someone please contact the M&M managment and ask them to fix this bug, so one can also book FlySmart awards?! Thanks in advance!!!
PS. HON Line was no help at all...