I have been using Manjaro since 2017 as far as I can remember. With rare exceptions, I have to restart the flash drive so that an option becomes available. I installed from Pahvo a few days ago and to my surprise, at one of the starting the flash drive, I only got the option of manually partition instead of Entire disk, Keep current. After several reboots all options appeared, and I was able to choose.
Well it depends which partition layout you have. kpmcore is a little fragile in detecting those, especially when LLVM was used. As a tip you can start calamares also in debug mode from the terminal.
I am afraid, I do not understand " kpmcore** is a little fragile in detecting those, especially when LLVM was used."/. I will have in mind the debugging mode for the future.