When a merge fast-forwards, updated files are marked with the status "U".
For example:

    $ got merge origin/main
    Forwarding refs/heads/main to refs/remotes/origin/main
    U  README
    Updated to commit 68883233da353be57c828e5667ffe68af3f9c32c

diff f6997150bbf387dd302b2fede9eeca6cee620f0f 722ff60be30844119fc3dc267b9087a4a5c177bc
commit - f6997150bbf387dd302b2fede9eeca6cee620f0f
commit + 722ff60be30844119fc3dc267b9087a4a5c177bc
blob - 4983f2ac232429e5c39c59d67d5fc268d186efd1
blob + 07259c7f157e0c5068d9619e97fed85a1e35311c
--- got/got.1
+++ got/got.1
@@ -3432,6 +3432,7 @@ While merging changes found on the
 into the work tree, show the status of each affected file,
 using the following status codes:
 .Bl -column YXZ description
+.It U Ta file was updated
 .It G Ta file was merged
 .It C Ta file was merged and conflicts occurred during merge
 .It ! Ta changes destined for a missing file were not merged