Look:
Ryzen 7840U replacement Framework mainboard £699 (currently discounted): https://frame.work/gb/en/products/mainboard-amd-ryzen-7040-s...
Thinkbook 14" Gen 7, 7735HS/16G/512G £730 - https://www.lenovo.com/gb/en/configurator/cto/index.html?bun...
Ideapad Slim 3 Gen 10 14", 8840HS/24G/512G £730 - https://www.lenovo.com/gb/en/configurator/cto/index.html?bun...
7840U and 8840HS are essentially the same CPU and the difference in performance between 7840U and 7735HS is minimal, few % at best. So these three are comparable. I'm sorry but for the price of a replacement mainboard I can buy a brand new whole laptop with memory, storage, screen, the everything that comes with it. Am I the only one who just doesn't get the hype behind a repairable laptop?