There will be no microtransactions in Gotham Knights

Yes, Gotham Knights is not a game service, as it was known from the beginning. But microtransactions could still be stuffed there. It would be possible, but the developers did not do it. 

Information about this came from the page with frequently asked questions on the official website of Hotham Knights. When asked if there will be microtransactions in the game, they answered: "No. Gotham Knights will have no in-game purchases or microtransactions."

Gotham Knights will be available for PC (Steam and Epic Games Store), PlayStation 5 and Xbox Series. The last generation was abandoned to give players a "better impression". 

Source: www.gothamknightsgame.com