What they meant is that MX150 is a BGA chip, meaning that it is available only as a motherboard-soldered piece. Your motherboard possibly has something looking like the place an MX150 would go into, but there are multiple problems:
- such laptop chips are not generally available to the customer. To build a working GPU you would also need multiple other pieces including memory chips, capacitors and other SMDs
- even if you got the complete set, you would need a BGA-soldering station to do anything with it. And those aren't cheap
- and even if you managed to solder it to the board, the traces to BGA socket are most likely dead, as Lenovo would not want to have exposed pads causing shorts, rusting, etc. Additionally, MX150 model of T480s seems to be using slightly different cooling assembly, so your current one wouldn't work for MX150 neither
