While up late one night wandering the annals of the internet I stumbled across a project called Ventoy that looks to be the king of bootable USB images. Simply flash the USB stick with Ventoy then simply copy to it whatever ISO files you would normally want to use individually. Then when booting off said USB key you are greeted with the following menu allowing you to boot into each ISO like it was flashed directly to the key. This allows you to make a USB key that has a mix of the Windows Installer, Macrium Reflect, Linux distros, Memtest, etc.
Check it out over at https://www.ventoy.net/