We are going to use SteamCMD. Is a tool for developers.

1. Download and run SteamCMD, extract in "c:Steamcmd" folder for example.
https://developer.valvesoftware.com/wiki/SteamCMD#Downloading_SteamCMD

2. Create a txt file with this content, replace the jpg and mod directory with the ones of your own mod, add your publishfileid from your old published folder inside the ItemizationQuest.icmod (open with text editor) if is not a new entry.

The Mod folder must contain your buildt mod, as a folder mine would be C:\Games\SteamLibrary\steamapps\common\Titan Quest Anniversary Edition\WorkshopTool\SteamWorkshop\ItemizationQuest\CustomMaps\itemization-quest

"workshopitem"
{
"appid" "475150"
"publishedfileid" "0"
"contentfolder" "C:\Games\SteamLibrary\steamapps\common\Titan Quest Anniversary Edition\WorkshopTool\SteamWorkshop\ItemizationQuest\CustomMaps"
"previewfile" "C:\Games\SteamLibrary\steamapps\common\Titan Quest Anniversary Edition\WorkshopTool\SteamWorkshop\ItemizationQuest\workshop_image.jpg"
"visibility" "0"
"title" "Itemization Quest"
"description" "Itemization quest bounce mod"
"changenote" "Initial Release"
}

3. Start CMD, go to the extracted folder and run once "steamcmd.exe", it will download a lot of necessary files and enter the command line mods for steam "STEAM>"

4. Login with your steam account: "login ninakoru yourpasswordhere STEAMCODEHERE"

5. publish/update your item: "workshop_build_item yourfile.txt"

And done! you successfully created/updated your mod!

I hope it helps!

BTW I got the info from this workaround for another game:

https://steamhost.cn/steamcommunity_com/app/602960/discussions/1/1646544161771479822/