What version of macOS are you using? If Big Sur or later, then you'll want to use OpenCore to select the boot.
For earlier macOS versions, if your GPU has boot screen support, then you can use the Mac's Startup Manager (hold option key when booting) to change the default boot os. In the Startup Manager, select the macOS that you want to be the default, hold the control key so the arrow turns into a circular arrow, then press return. But you could also just boot the select macOS and change the default in the Startup Disk preferences panel.