Hello and welcome to the Manjaro Community!
In order to help us to help you, a few command outputs will be requested so that we can see how you have your system set up. The first will usually be:
inxi --admin --verbosity=8 --filter --width
(copy and paste the output here, select it with the mouse and then click the </> button at the top of the reply window).
Also, the same procedure with:
lsblk -f
sudo parted -l
… it is also well worth reading this, if you haven’t done so already (it looks long-winded, but most of the important stuff can be found at the top):
As a tip: it is best to remove the “other” disk when installing either OS. This helps to avoid these conflicts. 
All the best for 2025! 