Join button disappeared from individual meeting event 'tiles' in Calendar

Hello Piotr_JJ   There is a past post in the community that addresses this issue with many comments, some of them may give you a clue about your situation:  https://techcommunity.microsoft.com/t5/microsoft-teams/missing-quot-join-quot-button-in-microsoft-teams-calendar-for/m-p/897254

There is also an item from our Answers.Microsoft.com site that with other suggestions. https://answers.microsoft.com/en-us/msoffice/forum/all/join-button-for-meeting-not-showing-for-teams/e24c7dd4-ae56-49c6-95ce-8bff906d34f7

Hopefully one of these links will give you what you need.  If not, reply back and we'll see if there are other comments from community members.  Thank you for being a member of the Teams community.