2.4G and 5G as separate networks on my G54

1. Your router doesn’t “flip” between the 2. It actually runs 3 networks simutaneaously. The 2.4g, the 5gh, and the 6gh. If you’re door lock doesn’t support 5 or 6, it won’t connect to them because it doesn’t have the hardware to even see them. I wouldn’t try to separate out the networks or it ruins the whole point of Wifi 7 (band steering)
2. What door lock is it? Models help
3. Most door locks are a bit of a challenge. The reason why is they tend to be mounted in steel doors. Steel is excellent at blocking wifi. It makes it a challenge to mount and be useful. 
4. They also tend to be battery powered and sensitive to low voltage or have periods of inactivity. 
5. I’d contact your door lock manufacturer before messing with the bandsteering. They’ll know more about their device and what needs to be done. I’ve been using mesh networks for over a decade and have 3 different locks. Contact the people who made the lock, not comcast 

You can only split the primary network; the guest network cannot be split. Once the primary network is split, you will have a dedicated 2.4 GHz SSID available for connecting your devices.

Please refer to the link below for instructions on how to split the network.

http://arris.my.salesforce-sites.com/consumers/articles/knowledge/G54-Multiple-SSIDs-Setup