Need someone to take their time and do this stuff, yes. People have tried in the past, including myself. Don't have the time anymore and people move on. Would be nice to see it revived though.

If that doesn't work - you could try installing CTF manually:
First you need to download the files (go to hl2ctf.com)
Shut down the Steam Platform
Open the HL2CTF .ZIP archive file you downloaded and run "Test Archive" to verify.
In the ZIP utility, select extract archive, from Explorer right-click on the ZIP and select "Extract to:"
Extract the archive with folders to your /SourceMods folder which will create the /hl2ctf folder.
Reload Steam and locate 'Half-Life 2: Capture the Flag 2.1' in your Steam Games Library.

Have you tried veryfiying source SDK files?