Dual Boot on iMac with Mojave/Catalina

I have an iMac 27" late 2017. I would like to install both Mojave and Catalina on my Mac. Should I partition my internal Drive (it's 1 TB fusion drive) and install Catalina with a usb flash on the new partition or should I follow another method?. IMPORTANT: I don't want to break the hard disk, or delete the OS, or format anything for error... Only partition the disk and install another OS on another partition... is it a risky operation? It is secure to partition my internal drive? Thank you!