User Hauke Reddmann noted in a previous answer that there should be a straightforward way to secure selfmate against a substantially weaker opponent (i.e., force them to checkmate you):
win all the ...
How quickly can a legal game reach a position where one side must
This is in effect Evergalo's reading (see
his (now deleted) answer)
of Rewan Demontay's Question 33154; that question ...