Your BIOS handles interleaving automatically.

Yes, the BIOS will configure interleaving (or flex mode) on its own. You don’t need to touch any settings.

Interleaving is handled by the memory controller built into the CPU. The BIOS just initializes it based on what it detects. If the soldered RAM and the replaceable stick are the same speed, size, and timings, the system will try to interleave them for dual-channel performance. If they don’t match, it’ll fall back to hybrid mode — part dual-channel, part single-channel. That’s the best it can do.

There’s no BIOS toggle for “enable interleaving” on consumer laptops. The only time you’d dig into settings is on some high-end workstation or server boards, and that’s not your situation. So plug in your new stick, let it boot, and trust the BIOS to do its job. It’s been doing this for twenty years.

You can check interleaving with CPU-Z or in the BIOS memory info screen, but there’s nothing to adjust.