Hello @Conigliaro
WiFi client devices decide which access point to connect to when multiple choices are available on a common SSID (network name). They are supposed to scan for all available access points, measure the signal quality from each, and pick the one with the strongest signal. Unfortunately, some devices just start scanning and connect to the first one they hear from, which results in a random choice. They may even remember which one that was and skip the scanning step next time they are power cycled and just reconnect again. I don't know if that doorbell is doing that or not, but it's entirely possible.
So, all of that said, I would suggest powering off the mesh points other than the one you want that doorbell to connect to. That may cause it to switch to the closer one within a minute or two. If it doesn't, you might need to power cycle the doorbell first. If that still doesn't get it to switch, then I would try doing a reset and reconfiguration (all while the other Nest WiFi points are off). Hopefully, that will get it to start with the one you want and (hopefully) stay there.
However, it's possible the next time it is power cycled, it will end up connecting to a random point. If that happens, I would hope just powering off those other Nest WiFi points briefly would be enough to get it switched again.
In my own network, I have a Nest Hello doorbell, and it seems to at least do a proper scan and selection to get connected to a reasonable access point (I have Google WiFi, but from the client's perspective, it looks the same as Nest WiFi or any other multiple access point WiFi network).
