Hi @Mark Do ,
There are N number of custom calendar apps in Teams were you can find what you need.
- You can create complete custom app to you requirement if need.
- But you cant deploy that into teams unless you have office admin permission.
- Be careful in using third party apps, because few app will collect your data. So try to use the apps which is created by verified company or read "Terms & conditions" properly.
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If this helps you Please mark it as answered and up-vote 👍.
Regards,
Nithin