Alternatives
If you use a Linux desktop other than GNOME, for example KDE Plasma or XFCE, then you cannot run GNOME extensions. (At least, out of the box.) The same holds true if you use a tiling window manager (Hyprland, Awesome, etc.).
If, for whatever reason, you cannot run the Draw On Gnome extension, here are some FOSS Linux alternatives:
gromit-mpx
This is a simpler program but it can run on any *nix-based system.
My Goto Backup
This is my backup drawing program in case Draw On Gnome fails.
ScreenPen
Another good alternative. This displays a clickable palette.
Xournal++
More of a note taking app.
OpenBoard
This is a whiteboarding solution.
Drawing
This is a Flatpak install. Written in Python, can work on any Linux distro or GUI.
DrawPen
This is a new development for Linux and other OSes. It has some real promise!