Given newness Ryzen 5 5600G, it was easy to presume you’re using UEFI to boot. Apparently you have at least one installed disk that saw life in an older computer, or you simply chose legacy booting over modern mainstream UEFI booting. Usurpation is avoided or handled rather differently booting legacy. A separate boot partition doesn’t affect this choice. Output pasted here, using code tags, from parted -l should be useful going further with this.
All my multiboot UEFI PCs boot using the method shown in this forum thread here. Similar could be done with legacy booting, but note the method uses a one bootloader installed per PC configuration, with a separate primary partition to which Grub is installed, and contains the Grub booting files. It doesn’t get mount it to /boot/, and it contains no kernels or initrds, essentially a one bootloader per PC configuration. It’s a low maintenance system due to making use of kernel and initrd symlinks on installed systems.