Power Automate "exists" in the "cloud", not your local computer, so it is not affect by your local computer setting.
If you simply "output" the dynamic content of a "number", it will only show the number: 11111.11
If you want it to look "good", you will need to do the formating specific for what you want to do, as Power Auotmate does not know if 11111.11 is a currency or just a decimal number. It doesn't know if you want $11,111.11 or 11,111.11 or £11,111.111
That said, what you want to "globally set" is not available on power automate. The easy thing to do instead of using the "format number" action for each number you want to display is to use the formatNumber() expression.
Say you want to send an email that shows 5 numbers in currency of UK format, you don't need 5 format number actions, just in the send email action, instead of directly adding the dynamic content for the 5 numbers, use formatNumber(the_1st_number, 'C', 'en-GB')
formatNumber(the_2nd_number, 'C', 'en-GB')
formatNumber(the_3rd_number, 'C', 'en-GB')
formatNumber(the_4th_number, 'C', 'en-GB')
formatNumber(the_5th_number, 'C', 'en-GB')
