Can confirm. At a former job I worked on a project with data warehouse sql tables that had 3 million rows. takes a while to perform meaningful queries on that, but it was fine with the technologies of SQL (our case Microsoft SQL)
For a FiveM server, MySQL is fine. You will not reach the limits of it. The choice whether you want mysql or not is another thing. If you make use of a lot of relations, a relational database lime MySQL is good. if you want to store data that has little to do with one another, then a flat storage system like NoSQL is fine too. Or even JSON i/o is quite fast on smaller data.