In 2017, Google tested out a new feature in Maps that showed speed limits in turn-by-turn navigation mode. This update, which was tested in 2 major cities, became less accurate over time, and was eventually axed over time. Now, it appears the app is trying this function out again. It is reportedly available to users in some parts of the US.
https://www.notebookcheck.net/Google-Maps-now-display-speed-limits-in-certain-areas.396376.0.html