Which Bootloader are you using, Clover or OpenCore? As they each have different methods to set the default boot drive.
I am not sure you can use any of these methods remotely. I think you have to be in front of the system to make these changes, as you can't currently boot in to macOS. I am assuming you can't see the remote systems Clover or OC boot screen, that the first screen you see is the login screen for Windows or macOS.
Clover:
You can set the default boot drive by adding the name in the config.plist.
This selection will remain after a NVRAM Reset, as it is coded in to the config.plist.
OpenCore:
You can set the default boot drive from the OC boot screen, press and hold the 'Ctrl' key then press the Enter key, while the macOS drive icon is highlighted. The up arrow icon, which sits below the drive icon, will change to a circular arrow when these two keys are pressed which indicates the macOS drive is now set to be the default drive.
This selection does not remain after a NVRAM Reset. But as you are working remotely on this system, that isn't likely to be happening if you aren't in front of the system.
MacOS:
Monterey/Ventura/Sonoma: Navigate to the System Settings > General > Startup Disk and select your macOS drive. You will need to enter your password to unlock this feature and make your disk selection.
Big Sur/earlier: navigate to System Preferences > Startup Disk and select your macOS drive. You will need to enter your password to unlock this feature and make your disk selection.
