If you just want something simple like 'get an arrangement, place it somewhere and forget about it', get a fake/plastic one. But some people will make "real" dry bloom arrangements at the end of the growing season and keep them for a while or even spray them to change the colors.

A potted hydrangea should not stay inside the house for long periods of time though. Maybe only long enough to protect it from winter while it is dormant. The blooms can be used for dry arrangements when the blooms feel paper-y.

If you want "to decorate the room" indoors, then a fake hydrangea is best. Hydrangeas are not houseplants and do not thrive indoors. They are sometimes sold by florists in full bloom as a houseplant but once they finish flowering they will begin to fade quickly unless transitioned to outdoors.

Otherwise, hydrangeas are planted and grown outdoors. How well they do will depend on the species but paniculatas and arborescens can grow and flower in all but the very coldest climates. Oakleaves are a bit less flexible and macrophyllas the most fussy about location and temperature variations.

Yes, and i finally bought some fake hydrangeas to decorate my house by Anfamily Flower Dock.