Wvpianoman
welcome to the forum.
lots of missing info here.
you installed it next to Garuda? grub and uefi in same boot are incompatible imo. something like that?
or did you give solus the whole disk?
did you prep the disk (format to gpt) before you installed solus?
black screen means bootloader or possible nvidia weirdness or disk not formatted right or a couple other things.
you should be able to get the USB live back by powering down then power up and hit F12 over and over til you get a boot menu. pick usb of course.
this is just a response to what I think I am understanding. Goodnight, hang in there. furnish more info and the calvary will come.
edit: also at Main Site at top of screen is a troubleshooting help section.