Launch installer from GRUB

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You have a couple of issues, with one drive.

You cannot edit partitions from working system. How are you going to modify partitions, or are you just wanting to install into existing partition. Even then if install fails for any reason, you have an unbootable system and no way to repair it. Always have a live installer, just for repairs, if needed.

If you boot using grub, the partitions you boot from cannot be changed by installer. And if grub install fails you have a non-bootable system.

I always have multiple repair/recovery flash drives like this:
https://discourse.ubuntu.com/t/beyond-grub-usb-stick-with-refind/67747
or
https://discourse.ubuntu.com/t/emergency-repair-disk/67791

You can use grub to boot ISO directly, or boot an extracted ISO.
You can create a FAT32 file as new ESP - efi system partition and directly boot using UEFI one time boot, an extracted ISO from that partition. But if issues with install & changing ESP back to the one you really want is often an issue, requiring terminal to unmount & remount correct ESP for new install.

I use grub to boot ISO on another drive, originally one of my many flash drive, but sometimes from HDD to install into SSD or from SSD to install into HDD as test install.

I have a folder /ISO where I store all my ISO and a file with boot stanzas that I call (configfile) from my standard grub to boot any of my ISO. Have not yet updated to latest ISO. The toram parameter may allow you to manually unmount partitions, but again any failure will require a repair flash drive.

menuentry "Kubuntu 24.04.2 Noble ISO" {
	set isofile="/ISO/kubuntu-24.04.2-desktop-amd64.iso"
	loopback loop (hd1,5)$isofile
	    linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile toram noeject
	    initrd (loop)/casper/initrd
}

more examples:
https://help.ubuntu.com/community/Grub2/ISOBoot
https://help.ubuntu.com/community/Grub2/ISOBoot/Examples

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