@Linda Garcia yeah this is a real concern and you're thinking about it the right way. The frequency separation helps but it doesn't make you immune — GNSS receivers are notoriously sensitive (we're talking signals around -130dBm from orbit), so even out-of-band energy from a nearby high-power transmitter can raise the noise floor enough to hurt fix quality or TTFF.
The honest answer is that 20-30mm is pretty tight if you're transmitting at full power. A few things that actually help in practice: a ground plane break between the two modules goes a long way, and if your layout allows it, orienting the GNSS patch antenna so it's physically shielded from the BLE module's antenna helps more than most people expect. Some builders also add a small metal shield can over the BLE RF section — not elegant but effective.
The other thing worth considering is whether your firmware can stagger transmit and GNSS acquisition — doing your satellite fix first, then keying up the BLE transmitter. It's not always practical depending on your use case but on a tracker that only needs occasional position updates it can basically eliminate the interference problem.
If you're still seeing issues after layout optimization, I'd start by checking your GNSS fix rate and SNR values during active BLE transmission versus when it's idle — that'll tell you pretty quickly whether you actually have a problem or if the separation is enough in your specific build.
