I’m no expert, byebyeapple, but I use rEFInd and I play around with various Linux distributions every now and then. Sometimes a new Linux installation will “hijack” the boot sequence and boot directly to the newly installed Linux system. To remedy this I go into my Dell PC’s BIOS settings and change the boot order so that rEFInd is number 1 again.
I assume you are using an Apple product and if so then I can’t be of much more help here. I don’t know how to change the boot order on an Apple system but I’m sure someone else can chime in.
Edit: And Yochanan’s suggestion to install manjaro-refind-installer may be all that you’ll need to do. Search for it in the software app “Pamac.”