Hi @JoeTheOne1
I don't think power fx allows a comma instead of a decimal. You could achieve what you are looking for with a series of replaces and #,##0.00 as your format.
replace(replace(replace(outputs('Format_number')?['body'],',','x'),'.',','),'x','.')
note I have replaced the initial , to an x in order to prevent the original , being lost


Damien