In my opinion, SQL Server 2019 is one of the greatest releases of the product that Microsoft has ever produced. The amount of improvements across the platform really allows data professionals to have better and faster queries while simultaneously minimizing effort. One of the many things that it fixes is the ability to get an actual plan without having to re-run the query.
Currently, if you are not on SQL Server 2019 and wanted to see an execution plan, you would attempt to dive into the execution plan cache to retrieve an estimated plan. Keep in mind that this just an estimated plan and the actual plan, while the shape should be the same, will have runtime metrics. These Actual runtime metrics could be, different than what is shown in the estimated plan, so it is important to get the actual whenever possible.