Should I seal a brick chimney breast on party wall
Usually the main purpose of a sealer is to protect against moisture. However, in your case the weather is not the issue, but rather appearance. 

Silicones were developed to penetrate the brick and provide a coating to protect the brick. Those sealers were rated by how much silicon was in the sealer...2%, 3%, etc. The more, then the more expensive. 

Clear sealers come in 3 types: 1) acrylic, 2) polyurethane, and 3) epoxy. 

1) Acrylic is the cheapest and probably best for your use. It not too thick so it doesn’t look like a coating, but still gives the finish and protection against dust, etc. 

2) Polyurethane will be too thick and give a thick appearance. 

3)Epoxy is used primarily indoors because it does not have any UV protection AND you can select a finish: gloss, flat, etc., but is a heavy coating that does not allow the wall to “breathe”. If you use an epoxy sealer, make sure the wall is extremely dry. 

Here’s an article that explains it better:

https://www.masonrymagazine.com/blog/2018/09/01/coatings-sealants-and-graffiti-protection/