I guess what is confusing me is why I can't just detach my external drive like I always do when I'm done with it and go into my OS on my internal drive minus the external drive being attached. I don't want to have to tell my Mac which drive to go into every time. Besides, there will only be one OS (Catalina or the next one) on my internal drive anyway. I've decided not to put more than one OS on my SSD as you've suggested. Plus, I have found that once I relegate an older OS to my external drive, I rarely go there again. Of course, I would be putting my new OS on the external drive, also. I need to keep this really, really simple as I do now. I honestly don't feel the need to back up everyday. There is nothing that important on my Mac that I need to do this and really don't want to.
If I were using a desktop computer it would be a simple thing to keep my external drive connected. I only have a laptop which I actually use on my lap. It's too awkward to keep the external drive connected because of logistics and it's short cable. It has come out of the USB port more than once because I had the audacity to move in my chair.
