Hang blackout curtains or drapes over the window
Install a tension rod and use a thick curtain panel
Apply removable window film or privacy film
Cover the glass with frosted adhesive film
Mount a decorative fabric panel over the frame
Use a large piece of plywood cut to fit the opening
Paint the plywood to match the wall
Attach foam board or rigid insulation board inside the frame
Cover the window with a tapestry or wall hanging
Place a bookshelf or tall cabinet in front of the window
Install interior shutters and keep them closed
Use blinds and close them fully
Apply contact paper or opaque vinyl to the glass
Hang a room divider in front of the window
Use a magnetic window cover if the frame allows it
Seal the edges of a removable panel with weatherstripping
Cover the opening with drywall if it is a permanent change