Startup issue while booting Windows from external drive
I have a 2017 Macbook Air, and I have installed Windows on my external hard drive so that I can boot my Mac into Windows. All that works fine, but the issue (which arose a few weeks after I first dual booted) is that when I try to boot back into MacOS Catalina, I get a black screen with a circle and slash.
I am, however, able to boot into MacOS after I run Recovery Mode and choose my internal hard drive as the startup disk. The irritating part is that I have to do this every single time I run Windows and want to switch back to MacOS. Is there any way I can fix this permanently? Also, is this potentially harmful in the long run?
PS: I have selected my internal hard drive as the Startup Disk within the Disk Utility app on MacOS as well, but that does not fix the issue.
MacBook Air 13″, macOS 10.15