Hi @Anonymous,
Do you mean that other users would be directed to the approval center to make a response when they click "Approve" or "Reject" button within Outlook email?
I have made a test on my side and I could make a response within email and complete the approval flow. The flow works successfully as below:

Please check if the other users update their Outlook client to the latest version, if not, please consider take a try to update their Outlook client to the latest version.
In addition, please check if the other users's Outlook client meets Outlook version requirements for actionable messages. Please ask other users to check if their Outlook client meets Outlook version requirements for actionable messages with following article:
Outlook version requirements for actionable messages
More details about Actionable messages in Outlook, please check the following article:
Actionable messages in Outlook
Best regards,
Kris