Raspberry Pi is actively preventing enthusiasts from upgrading soldered memory to a larger configuration even when the replacement chip is technically compatible. The company says the restriction is intended to discourage unofficial high-capacity resales.
That’s my experience too.
That said at the higher end (Raspberry Pi 5) its actually cheaper to get a Mini-PC with a low-power intel chip like the N100 than a Pi and it’s more powerful, more extendable, more compatible, with a much better and well supported tech stack (because that’s an actual PC) and you get the whole device already, not just a board that you have to add the box and everything else to make a computer from.
Maybe at the level of the little SBCs the rp2350 is good value, but that stuff is more towards the embedded systems side (high end, though, beyond things like ESP32) than a general consumer computer.