I installed R4.0.4 in a primary partition alongside a linux Mint ext4 partition, both of which comprise <20% of my 2TB SSD. (Thanks to MS-Win[*], I never park proprietary files within an OS slice, opting instead for the relative safety of logical drives resident in an extended partition.)
My intention was to retain a fall-back OS during my Qubes evaluation, but quickly acquired qube-legs such that I never got around to altering grub.cfg to include the Mint vectors. So I scrapped the Mint slice and expanded Qubes proportionately. Qubes works mighty fine, and I have acres of storage to play with.