The Nintendo Switch is region-free (with the exception of Chinese Nintendo Switches - see below). As the link states:
Nintendo president Tatsumi Kimishima confirmed the system won’t be region locked, meaning players will be able to play globally released software on the console-handheld hybrid.
The Wikipedia page for the Switch explains further:
Unlike previous Nintendo home consoles, the Switch is region-free. This allows players to use cartridges or downloaded content from any part of the world, with the exception of Chinese game content which can only be played on Switch units manufactured for that country. Nintendo recommends using the appropriate regional eShop for digital purposes for obtaining the best post-purchase support if needed.
Officially, in 2019, the Nintendo Switch was released in China with the aid of Tencent. In China, all Switch games are published by Tencent, and are regionally locked out from other global Nintendo Switches (meaning they will only work on Chinese consoles).
Earlier this week, it was revealed that physical game cards released for the Tencent Nintendo Switch in China won’t be playable on global Nintendo Switches.
However, these Chinese variant consoles can play other non-Tencent produced games, however only in offline mode:
Meanwhile, the Tencent Nintendo Switch will be able to play global game cards, albeit only offline. This is because the Chinese variant will go through its own servers.
Additionally, Tencent will help to run the online services within China, according to Wikipedia:
Tencent will help localize various titles, and help implement the Nintendo Switch Online service within the country, integrating its offerings with the WeChat payment systems