Using of mfind in general case : with or without extension for substring of a filename, even with a number
You are using mdfind correctly, but apparently there is a problem with your Spotlight indexes.



I attempted to reproduce the behaviour you observed, but it seems to work fine for me. In fact I got exactly the same results as user3439894.  First I created a sample file having the same name as your file.

touch GCph_WL_FoM_154.46_AND_SIMPLE_SUM_GCsp_XC_AVEC_NO-ZCUT_FoM_571.35.py


Then I tried two different search commands. Both of them produced exactly one result: the file created above.

mdfind '154.46'
mdfind -name '154.46'


I also tried your third search command, but it yielded nothing because the search term was incorrect. Here it is again, fixed, with * asterisks for wildcard globbing.

mdfind 'kMDItemFSName == "*154.46*"'


This is the answer to the question you asked originally. If you want a different answer, please edit your post to focus on one question.