They are called Periodic, or Frequent Batch, auctions.
This paper & earlier works it's based on were very influential in the design and regulatory framework for these: https://academic.oup.com/qje/article/130/4/1547/1916146
Here's a good intro to them: https://www.fca.org.uk/publications/research/periodic-auctio...
Volumes are small relative to the market as a whole, but execution quality is very good.