I've never seen Cura add a negative Z value.
Here is your startup gcode:
Are you running OctoPrint? Everything is commented out except the last line.
That last line appears to be missing the "close curly bracket" at the very end.
The only post-processor I see running is Insert at Layer Change is that correct?
I added a little tube next to my model so something is touching the buildplate and now the print starts above the build plate but support-brim is missing
/edit: it works again after I enabled skirt - before it was set to 'none' as I don't need print a skirt when support-brim is enabled
this is how 1st layer looks in Cura 5.2:
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