Above formula returns #VALUE! instead of a correct result because FINDROW condition interpreter fails to convert a picklist datatype to a datatype that can compare to the datatype on the other side of the operand.
Thanks for this feature request post @FlyingZebra ! Your feedback is important to us as we continue to find ways to improve experiences for our users. I'll bring this feedback to our team about comparing picklist vs plain text formats.
Glad you were able to find a method for your formula, but also wanted to share another way to accomplish this. Since you are unable to compare two different formats, what you can do is retrieve a rowlink’s column (dereference). In you case, you can rewrite this formula =FINDROW(_Req_Type_5,"_Req_Type_5[Name]=[Req Type]")[Process] to this instead:
What this does is pull the [Name] data from the _Req_Type_5 table for the rowlinked column [Req Type]. Since the [Name] data from the _Req_Type_5 table is text format the formula should work as well.