Hi @ NickSz,
Could you please share a screenshot of the configuration of your flow?
What is the type of the “category column” that you mentioned?
If you want the flow would be triggered when an item is created in the sharepoint list and the value of the category column is equal to a value such as “A”, you couldn’t achieve it until now, because Microsoft flow could support trigger a flow with an item currently, and trigger a flow with an column is not supported in Microsoft flow currently.
However, you could add a condition under the trigger to check if the value of category column is equal to “A”, if the category value is equal to “A”, then send the email, else if the category value isn’t equal to “A”, do nothing.
I have made a test on my side and I have created a sharepoint list as below:
The “category” column is a choice type column with value “A”, “B” and “C”.
I have created a flow as below:

When an item is created in the list, and the value of “category” column is equal to “A”, the flow would run successfully as below:

Regards,
Alice Zhang