Before I buy this expansion...

[caketastydelish]

Are there any high-quality WW2 mods available for it?

 

[Victoria]

Are there any high-quality WW2 mods available for it?

Civ VI is not really a good combat simulator so hopefully you are just wanting a 2 player scenario or similar.
If you put your question in the title or in the modding forum you will get a faster response... I think @Gedemon would be able to give a fair answer.

 

[Gedemon]

There is the Relive World Wars mod maybe, but I've not tested it yet.

Edit: and it's for the vanilla game.

 

[Deliverator]

Are there any high-quality WW2 mods available for it?

JFD had a few WW2 Leaders and Civilizations but apart from Stalin I don't think they've been officially updated for Gathering Storm. The others such as Mussolini, Hitler, Churchill and de Gaulle may work if you ignore the compatibility warning.

 

[Deliverator]

There is the Relive World Wars mod maybe, but I've not tested it yet.

It looks like that mod was updated post-Gathering Storm with the Ottomans etc. Last update is 25th March 2019.