This is correct, the SN770M is not compatible with the Lenovo Legion Go as it is an M.2 2230.
The Lenovo Legion Go requires an M.2 2242 SSD: https://legiongolife.com/how-to-upg...
According to this article, you also need an adapter to clone the SSD of the Legion Go.
On Galaxus/Digitec I cannot currently find a larger SSD for the Legion Go than the one installed, at least none that is available.
However, you may be able to find one from another supplier :)

Hello,
I installed this ssd on my legion go.
But I had to use an M2 2230 / 2242 adapter.
The adapter was found at another vendor.
It is also necessary to provide a USB nvme box to clone the SSD of the legion go.
Best regards

The Legion Go unfortunately does not have a 2230 screw slot. There is a tape that can hold the memory, but if you want to frank effectively there are extenders for M.2 from 2230 to 2242 like this one: https://www.amazon.com/NFHK-22x30...

or online there are 3D models you can print out to extend the back so you can screw the screw into the 2242 slot.

I saw on YouTube that it's possible to find 2230 to 2242 adapters that allow you to use the SN770M in the Legion Go. I'm not sure if it works, but it's worth investigating on the internet.