Has anyone had issues or a solution to slow performance when running the game windowed?
I think its caused by updating to the latest AMD Drivers 24.10.1
Previously it was working fine when in Windowed mode,, and i though the issue only started on a specific mission but when testing the issue occurs when starting a new campaign.

Checking further reveals that the issue occurs when the game is launched with "Warcraft II BNE_dx.exe".
But works fine if started with "Warcraft II BNE.exe" in the game folder.

I encounter the slow down issue when loading a save, or starting a new campaign.
The entire game appears to lag (Even menu and cursor movements are delayed), the main menu of the game works fine without any issues.

Strange that happened in windowed for you.
Try experiment with wrapper setting, available from dxcdg.exe or regular Launcher. Run them by Run as Admin command (and if you have Galaxy(Bnet)/Warcraft installed to Program Files - afterwards start Wc2 as Admin too).

This issue has been fixed with the latest update.

Can confirm, except I had the issue in full screen mode.

Updated AMD drivers to 24.12.1 and the "GOG Enhanced" version of the game now plays fine.

UNFORTUNATELY, the CLASSIC version of the game starts and goes in-game but then locks-up after a few seconds.
The music continues playing but the game is unresponsive.

Another reason why I went with the gog release of the game instead of Blizzard's.

I've updated to the latest driver, it still runs like ass