How do I watch old demos after x64?

[Tiftid]

I have downloaded 1.09 GB of cp_bruhstbowl demo files with the idea of rewatching them and finally getting the "Friendly Fire Incident" on video.
However, it appears to be impossible to watch pre-25/07/2023 demos after the x64 update.
If you install one of the compatibility beta clients, you get hl2.exe instead of tf_win64, causing TF2 to not open through Steam.

Attempting to manually open the exe gives this error after the opening movie:

In case you're wondering, restarting my computer and verifying integrity of game files does NOT fix this problem.

What DLL am I missing? Where do I download it? And can someone remind me why x64 was a good idea again?
Answers to these three questions would be much appreciated. Cheers.

 

[Plainz]

have you tried launching the exe with steam set to offline mode?

 

[Tiftid]

have you tried launching the exe with steam set to offline mode?

I have - it has changed nothing. It's not a Steam API problem, it's a missing DLL and I wish I knew which one.

EDIT: It seems like this problem usually pertains to the game being unable to locate client.dll and server.dll.
However, both of these files ARE present in the beta install, and gameinfo.txt does point to tf/bin which is indeed where these two files live.