I'm interested in purchasing a Lenovo Legion 5 laptop (Legion Pro 5 16IRX8). In the manufacturer's technical specifications sheet, it is mentioned that the laptop has slots for 2 SSDs (Up to two drives, 2 x M.2 2280 SSD up to 1TB), but from what i can understand, this is just what Lenovo offers. Will SSDs with larger capacities work? I'm interested in adding 2x4TB SSDs (after purchase of course).
You are correct, you can put larger drives in the slots, the 1TB is just what Lenovo offers as part of the spec. You will end up with the pre-installed SSD extra, since most laptop manufacturers don't offer to ship with no drive installed, but you can just turn it into an external drive with an inexpensive NVMe USB enclosure (Amazon or similar)
I would also recommend having a look on youtube for "Legion Pro 5 16IRX8 tear down" guides so you know what you will need to do in order to replace the drives. A quick review shows there are several and the procedure looks pretty straight forward - , just make sure you fully shut down the laptop and disconnect the battery before you remove/replace SSDs.