why is plural form here?
Nie lubię mówić na konferencjach -> I do not like to speak at conferences
Because English. It could also be "I don't like to speak at a conference." But that sounds a bit wonky in English. English prefers to use the plural for this construction. Apparently Polish prefers the singular.
"I do not like to speak at the conference"
Works. Although frankly, both sentences would make more sense with plural conferences.