What does it show when you tap on the “McDonald’s” right below the amount? It should show the unadjusted merchant name as opposed to the cleaned up version.
If that indicates the proper name then there’s something wrong on Apple’s side in terms of detecting the correct merchant and you can report it to be corrected.
If however it shows something indicating McDonald’s, then the merchant is using a terminal that is signed up with the wrong name.
They’re not supposed to do this, but it’s not entirely uncommon.
Both McDonald’s and Subway are franchises, and the franchisee might’ve signed up as a McDonald’s and later reused the terminal when they became a Subway franchisee (at a different location) or they might simply run two franchises under one company name (e.g. Johnson Food Services, LLC) and didn’t bother to get a separate contract under the Subway name.