Hi @Anonymous,
Could you please share a screenshot or more details about your form?
Could you please share a screenshot of your flow and the run history of your flow?
I have made a test on my side and don't have the issue that you mentioned.
I have created a form as below:

Then I have created a flow as below:

The expression in the Compose 2 as below:
formatDateTime(outputs('Compose'),'HH:mm tt')
The flow would run successfully as below:

Please ley me know if your problem could be solved.
Best regards,
Alice