Power Query M - If Row is equal to another row in different table

Hello,

I have these two tables:
TABLE1

TABLE2

I need to add a custom column to TABLE 1 that would check if KEY in TABLE 1 also appears in TABLE 2 then it would do something.

The name structure is the same, I need to do it in Power Query M.

I thought something like this would do that trick, but it seems I can't properly reference the other table's column:

if [Key] = (#"Backlog_Linked Issues"[Key]) then "Incident" else "Proactive"

I know it's a bit silly, but can you please help me with this IF Statement?