Looking at the memory limits and other limits on the SQL Server versions over time, we have seen things increase, but one limit that is still very low is the memory limit for SQL Express. Specifically the maximum memory for buffer pool per instance of SQL Server Database Engine for SQL 2019. The limit there is 1410 MB.
At first glance you may think that this limit is the total amount of memory that SQL Server will use, but let me show you a couple of screen shots for Database Health Monitor showing the memory utilization on two different SQL 2019 Express servers.
Read on to see what, exactly, the memory limitation is. Also, there are separate limits for things like In-Memory OLTP table sizes.