I hope and wish I'm mistaken but as far as I know unless the mod you are interested in from the Steam Workshop has a link to nexusmods or github for it, you are in general out of luck.

It is a pity, for games that sell in more than one platform that some modders decide to publish their work in steam's.

It is possible to use steam workshop mods with the Epic game version but it takes a few extra steps.

First, you need to download the mod itself. There are websites that allow downloading by copying and pasting the URL of the workshop item to their website. I've been using steamworkshopdownloader.io successfully so far. Failing that, you require a friend or *someone* to upload the pack files for you.

Due to a quirk or some-such of the above workshop download method you need to use some kind of hex editor and edit the unzipped and downloaded .pack file. Delete everything at the start of the file until you get to the P and stop, leaving the P in place. For this I've been using HXD. If this step isn't done the game will crash to desktop on launching if the mod is placed in the data folder and the pack editor won't be able to load the file.

Thirdly you need a pack editor to edit the .pack file and change it to a movie type instead of a mod. If you don't change the mod to a "movie" the game ignores the mod and doesn't load it. PACK RPFM is useful for this. Once it is a movie type, the .pack file needs to move to the total warhammer data folder.

The above is striked out because I have since realized this method may not be required. It turns out I had a typo on the user.script.txt file name originally which meant the load ordering was being ignored completely. I suggest setting to movie as last resort if the load order can't be setup correctly. Setting mods to Movie mode can disable some parts of mods too, although when playing with a large mod set with a friend we never noticed anything amiss.

Navigate to %Appdata%\The Creative Assembly\Warhammer\scripts. In this folder create a user.script.txt file.
For each mod you want to enable you add a new line that looks like this: mod "modname.pack";

Mod load order should be based on alphabetical order as usually mod authors will name their pack files in a particular way to ensure a reasonable load order.

After that the mod will load. Bear in mind not all mods work together nicely due to compatibility issues etc. This has worked well for me in single player and multiplayer using a combination of 48 mods, merged/edited where necessary to resolve conflicts. When playing multiplayer make sure you both have the exact same files in the data folder and the same load order in the user.scripts.txt file.

Cheers and have a good one.