Feedback is both singular and plural, like deer and fish.
"Feedback" is an uncountable noun so it doesn't have a plural form.
The plural form for the noun workshop is workshops.The noun feedback is an uncountable noun with no plural form; for example:"The feedback was retrieved." and, "Feedback is valuable to scientists."
There is no plural form for the word, countries. This word itself is a plural.
The plural form of the word "inferno" is "infernos."
There is no plural word for if.
The plural form is data.
There is no 'plural form' of the word 'minute'. The word is both singular and plural.
The plural of diary is diaries.
The plural form of the word gelato is gelati.
The plural form of the word "baby" is "babies."
The plural form for the word 'pioneer' is pioneers.
The plural form of the word signal is signals.