When using the Subject filed in the When a new email arrives in a shared mailbox, it can only be used to search for the presence of specific words in the subject of an email. It seems that a function cannot be detected here.
For your scenario, you could try to use a Condition in your flow to filter the subject that contains certain words.
Please have a try with a Condition on your side and if you need more help, please feel free reply.
Community Support Team _ Mabel Mao If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.