Flex mode handles it fine.

Yes, your system will use all the RAM. The higher-capacity module won’t be ignored. But dual-channel memory only works on the overlapping capacity.

Here’s how it shakes out: say you have 8GB soldered and add 16GB in the slot. The motherboard will run the first 8GB from each in dual-channel (your soldered 8GB + 8GB of the new stick), then the remaining 8GB from the new stick runs in single-channel. That’s called “flex mode” or “asymmetric dual-channel.” It’s not ideal for latency-sensitive tasks, but for most real-world use — gaming, productivity, multitasking — the performance hit is small. You still get more total memory, which matters more than perfect dual-channel symmetry.

The only time this backfires is if you mix drastically different speeds or timings. But if the new stick matches the soldered RAM’s specs, you’re fine. The system won’t prioritize one module over the other in a dumb way — it just makes the most of what you gave it.

Don’t overthink it. More RAM > perfect dual-channel, unless you’re benchmarking for a living.