The British Museum
I visited the British Museum in December 2019. Compared to the exhibits from other areas of the globe there is a modest African selection in the basement but includes some extremely valuable artefacts from outside of the Congo such as the 13th Century Benin Bronzes from the Edo peoples (shown below).
With respect to the Congo itself there are a number of exhibits including Kuba and Luba masks and a Katanga cross.
The world famous Museum is worth a visit of course and it has some excellent African artefacts.