Hi Sonia,
I'm not sure this option is available. You can try submitting this feedback directly to Microsoft via:
https://feedbackportal.microsoft.com/feedback/forum/ad198462-1c1c-ec11-b6e7-0022481f8472
Currently, favoriting people's chats/contacts is only available.
If this is helpful please accept answer.
Thank you for your answers.
Please confirm that MAKE IT AS FAVORITE option has been deprecated in Teams since there are a few videos and trainings that show option is or was available.
Here is a link to video https://www.youtube.com/watch?v=B7-vU36xNt4 and link to Learn that show that option https://learn.microsoft.com/en-us/training/modules/create-manage-teams-channels-microsoft-teams/4-manage-team