QuoteRAM is generally upgradeable on Intel variants just fine but they use DDR5 4800 instead of LPDDR5/LPDDR5X 6400. If they used DDR5 4800 for AMD then performance would be solidly weaker than Intel (Ryzens are hungry for fastest RAM possible), thermals would be slightly higher and battery life would be about the same as with Intel. Then people wouldn't be happy again so whatever they (Lenovo) do it's not good, someone will always be unhappy.
Now laptops come with ddr5-5600 kits with AMD processors. And the battery life is hardly affected. The problem with soldered RAM in laptops is its life cycle and future proofing. If you buy this laptop for professional workloads like video editing or CAD projects, they will quickly become outdated as that software consumes a lot of RAM today and in the future.
QuoteWith LPDDR5 6400 you also get about 15% better performance over DDR5 4800 just on the 680M/780M iGPU alone - youtu.be/F7VV_PxuLws - so if you want to disable this RTX 4060 here and use just integrated graphics you can enjoy in more graphics power and with longer battery life just because of soldered faster RAM
Also consider the iGPU use some memory as a simulated dedicated graphics card. For example, the iGPU 780M uses 3GB of memory to work with video rendering and encoding, especially when it comes to gaming. So you actually have almost 12 gigs of RAM to work with, if this laptop, for example, comes with 16 GB of soldered RAM.