There's a spreadsheet [0] tracking Switch games where you can see which ones have 'complete' versions on carts. It's roughly 1/4 for both first party and third party titles, though first party games are more likely to have cartridges released in a later run with updates included, while third party games are more likely to just have no updates.

(Splatoon Raiders was released a week ago so I don't think that's a good example to use for games without updates. Even it has an update already, albeit a non-critical one)

[0] https://docs.google.com/spreadsheets/u/0/d/1CEABCBrPv1tWf89h...