In the service manual for the HP 250 G9 HP claims RAM is “not customer accessible or upgradeable.
https://kaas.hpcloud.hp.com/pdf-public/pdf_5491984_en-US-1.pdf
HOWEVER, in the same service manual there is a procedure with pictures describing RAM upgrades. I’m sure it is technically upgradeable, but they claim it is not “customer upgradeable”, because you need tools to disassemble the laptop to perform the upgrade, which I a task for pros, not everyday customers.
They don’t claim anywhere that RAM is soldered onto the motherboard.