Cannot share calendar - people not receiving the invite

Hello, I cannot share my iCloud calendars with anyone. I invite people following the steps from this guide (Udostępnianie kalendarzy iCloud na iPhonie - Wsparcie Apple (PL)). But they never receive the invite. But if the same people invite me to their calendar, it works fine and I can see their calendars.

I have tried sharing to people using @icloud account and @gmail account. Same issue for both.

I have tried switching the email account for sending receiving invites from my gmail account to my iCloud account and it didn’t work on either.

I have tried using my iPad, iPhone and mac for this, same issue on all devices.

Please help me debug this, I’m getting desperate.