Hi @Sun, Spencer
Great to know that the issue has already been resolved and thanks for sharing the solution so that others experiencing the same thing can easily reference this! Since the Microsoft Q&A community has a policy that The question author cannot accept their own answer. They can only accept answers by others, I'll repost your solution in case you'd like to Accept the answer.
Case Title: Trouble selecting users in Teams to send Praise
Issue Symptom: Trying to send a Praise to some users in a Teams channel, but something is preventing me from selecting any users.
Resolution: Praise cannot be used in private channels, you need to use this feature in standard channels.
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