You have to enable them in options.
Options > Game > Enable Modded BDCC Launcher
Refresh after checking that and it will take you to the mod launcher there, click the "Mod Browser" button and you got a cacophony of mods to go through then, click "download mod" at the very top of the description preview window for any you want. Do be aware some are more outdated than others and so likely won't work or will even break, some outdated ones don't get screwy tho, so it's a better judgement thing. There are a very few that need a specific character datapack too, so go through that when you're able to check it out as well for any missing character models.
Enjoy your mods!