On the T16 I have one soldered RAM slot and one replaceable. Of course the SSD can be upgraded too.
The P16 (not the P16s which is just a T16) has four upgradable RAM slots and two slots for SSD.
So that’s not crazy amounts of upgradability but it’s something.
I actually got a Legion Pro 5 instead because it’s a lot cheaper but still has 2 upgradable RAM slots and two SSD slots. My only complaint is that the keyboard is less stable than on a thinkpad and it looks like a gaming laptop.
Someday I’ll get a P16 though… or else one of those Eurocom laptops, if only they had 16:10 screens and nice keyboards.