In Power Automate if you enter the dynamic content value from a lookup column typically you just get the GUID or if you select the dynamic value of a choice column you just get the ID number for that item.

Here is an example expression you can use to get the display name instead:

outputs('Get_a_row_by_Opportunity_ID')?['body/_modifiedby_value@OData.Community.Display.V1.FormattedValue']

The annotation @OData.Community.Display.V1.FormattedValue is the important part that can be added after the _value.

Here is how I build this out for my flows using Modify By as an example

Create a compose action and select Modified By (Value) as the dynamic content

Click the … and select peek code

I then copy AFTER the @ symbol and stop at the last double quote like so:

I then paste into notepad and add @OData.Community.Display.V1.FormattedValue after value:

Copy what you have created and it in the expressions section and click OK and you are done:

Reference:

https://linnzawwin.blogspot.com/2020/07/get-lookup-display-name-and-option-set.html