Hi there, Cieloooo_.
It appears that you're having a problem setting up your Epson L120 printer. You get an message that an error occurred when trying to add the printer, and we're glad to help with this.
Solve printing problems on Mac - Apple Support -- This page of the macOS User Guide provides steps to use when you're having problems connecting with your printer.
Epson L120 | L Series | Ink Tank Printers | Epson Philippines -- You may need to update the drivers for your printer.
Epson L120 | L Series | Ink Tank Printers | Epson -- See if you find any information about setting up your printer with your Mac in Epson's User Guide.
macOS Big Sur 11 Support | Epson US -- If you're still unable to connect the printer, please contact Epson Support
Take care.