For legitimate players, purchasing the on the eShop or buying the Overcooked! All You Can Eat physical edition for Switch is the cleanest way to get everything.
Overcooked! 2 on Nintendo Switch: The Ultimate Guide to Updates, DLC, and NSP Content
Here are some key details on what's included in the update and DLC:
Never download an .xci file labeled as "DLC" or an .exe file claiming to be a Switch game. Real NSPs are large (1GB+ for DLC) and open with archivers like 7-Zip to reveal .nca files.
2 - Season Pass. 4/18/19. DLC bundle. $6.79. $19.99. -66% Games. Overcooked! 2 - Too Many Cooks Pack. 8/7/18. DLC. $1.19. $2.99. - Overcooked! 2 - Nintendo Switch - Games
If you haven't bought the game yet, All You Can Eat is a better value ($39.99 retail). But if you only want Overcooked 2 and its expansions on your CFW Switch, the NSP/Update/DLC combo remains the gold standard.