I'm diffing two directories, 220 and sue, as follows:

diff -r 220 sue > diff.txt

The directory looks as follows afterwards:

$ ls -al
total 20
drwxrwx---+ 1 Administrators Domain Users     0 Jun 24 10:44 .
drwxrwx---+ 1 SYSTEM         SYSTEM           0 Jun 24 09:52 ..
drwxrwx---+ 1 Administrators Domain Users     0 Jun 24 09:54 220
-rw-rwxr--+ 1 jempty         Domain Users 15463 Jun 24 10:44 diff.txt
drwxrwx---+ 1 Administrators Domain Users     0 Jun 24 09:55 sue

Confirming diff.txt is text as follows:

$ file diff.txt
diff.txt: HTML document, ASCII text, with very long lines, with CRLF, LF line terminators

The above is primarily to demonstrate that I can use diff and see that there not a tremendous amount of differences.

Then creating a patch file as suggested by https://docs.moodle.org/dev/How_to_create_a_patch:

$ diff -Naur 220 sue > patch.txt

Results in the directory looking as follows:

$ ls -al
total 133836
drwxrwx---+ 1 Administrators Domain Users         0 Jun 24 10:57 .
drwxrwx---+ 1 SYSTEM         SYSTEM               0 Jun 24 09:52 ..
drwxrwx---+ 1 Administrators Domain Users         0 Jun 24 09:54 220
-rw-rwxr--+ 1 jempty         Domain Users     15463 Jun 24 10:44 diff.txt
-rw-rwxr--+ 1 jempty         Domain Users 137024100 Jun 24 10:57 patch.txt
drwxrwx---+ 1 Administrators Domain Users         0 Jun 24 09:55 sue

As you can see the patch.txt file is enormous and as it turns out it's binary:

$ file patch.txt
patch.txt: data

Should I be using the patch command instead of diff