What should we do to make our fireplace look less gloomy?

If you block it up with plaster board you must put a vent in the plasterboard, also I would put a cap over the chimney pot to stop any birds nesting. Prior to that I recommend a chimney sweep to see if anything is blocking the chimney and you have good air flow as if you have a bird nest you will get damp in the chimney,, so first job is to get it swept by a professional chimney sweep

It all depends on what look you want tbh, it's a shame to hide an original feature of the house and they can be revamped if wanted to. It is possible to board over it but if theres an existing chimney being boxed in it will need a vent to stop damp patches appearing later.

If you wanted to keep the Fireplace on show I would block the Flue with a Chimney balloon, as has been mentioned get it swept and a Cowl put on the pot so in the future you could just pull the balloon out and use it again.

Open it up. Paint inside. With a chimney balloon. Take balloon out in summer to help house vent..they only 35 quid..you can put so much stuff in opening.. Mark innes. Innes construction