Soldered plus two socketed slots doesn't give you triple-channel.

The short answer is no — at least not in any consumer laptop I’ve seen. When a laptop has soldered RAM and separate SODIMM slots, the memory controller still treats it as dual-channel. You get either one soldered stick plus one slot (asymmetric), or two soldered sticks plus two slots (symmetric), but always in pairs. Triple-channel was a desktop thing from a decade ago (Intel X58) and never made its way into laptops.

The flexibility comes in capacity, not speed or channel count. For example, a laptop with 8GB soldered + one empty slot can take a 16GB stick for 24GB total, but it’ll run in dual-channel only for the first 8GB+8GB (or similar), then single-channel for the remainder. If it has two slots and two soldered sticks, all four ranks can split into two channels — still dual-channel, just more memory.

If you actually need triple-channel bandwidth, you’re looking at a workstation desktop, not a laptop. For most people, the real benefit of soldered+socketed is being able to upgrade later without sacrificing the slim design entirely.

Bottom line: Don’t hunt for triple-channel laptops — they don’t exist. Just check whether the RAM configuration lets you add enough capacity for your workload.