One save per accounts but you can have multiple accounts on your console easily.
And I could recall wrong but I think other accounts(specifically ones without a nintendo ID of their own that are on the same console that your nintendo ID list as your "primary" switch console for cloud saves/etc) can still access the same DLC content that was purchased with your console without needing to buy DLCs twice so you can functionally use these accounts for separate game saves proper.
I mean I recall being able to access expansion pass content in Zelda on Switch in accounts others than the ones I purchased the DLC with.
So if you were worried...
Yes there's only "one" save but if you really want to be technical there are still as many saves as you want. Just that you need to split them in separate users account.
Tbh back in the 80ies we didn't have multiple users profiles able top support game saves of their own.
As mentioned in my other comment you can have separate saves by making multiple users profiles.
I can even confirm that on Switch DLCs aren't even a worry in that regard. I purchased the expansion pass DLC in Zelda and still accessed it's content on profiles on my console other than the eshop account I purchased the DLCs with.