Windows Server 2019 will get updates until Jan 2024. After that date it will continue to get security and critical updates until Jan 2029 (10 years) but will not receive new features. This is standard for Server OSes.
At this point if you're running a Server 2019 machine then you are fine until 2029. If you are looking at setting up a new server you should consider looking at Server 2022 instead which is the newer version and will remain in mainstream support until 2027 (estimated). However if you already have a 2019 license and want to stick with it then you can. But since 204 is coming up fast it probably makes sense to switch to 2022 to avoid having to readdress this in a few years.