At that point it seems almost worth it just to buy another one so you have two laptops; a mainboard has to be a significant part of the cost of the whole system.
(this was my problem back when I built desktops - it was almost never worth upgrading anything but RAM or disk, instead build a whole new one and repurpose/sell the old one)
It's something like a little under half the cost or so, last I checked. Not a terrible option if you're happy with the screen/keyboard/etc. bits you'd be keeping. And the one you take out can be repurposed into a mini-PC of its own, or sold.
As a desktop builder myself, I like the flexibility to upgrade (or easily replace for broken components) within the socket family (AMD in particular had a pretty wide run of compatibility recently with AM4), and even when doing a more "total" replacement down to the motherboard I could keep a good case, power supply, GPU, peripherals, etc. Just the fact that I have similar decisions open to me is interesting in the laptop space. The direction of the laptop market has otherwise been away from allowing even RAM or SSD upgrades, or making them tedious and onerous even if possible.
The repairability is a bigger thing for me; the upgradability is a nice plus (especially if you blow your motherboard, and need to buy a replacement, why not get the latest and greatest).
A built Framework 13" with a 13th gen intel CPU starts at $1050. Or you can grab the same mainboard for $450. For me, that's really compelling. And if you're upgrading (rather than replacing a failed component) you can still sell the old mainboard or use it as a server, etc. Not to mention the reduced ewaste compared to buying a whole new system.
(this was my problem back when I built desktops - it was almost never worth upgrading anything but RAM or disk, instead build a whole new one and repurpose/sell the old one)