Pterodactyl is a commonly used one as the other comments say, but just to give some background, Pterodactyl itself, rather than being a minecraft server hosting software, is actually a generic server hosting software that can be used pretty effectively with a lot of games or even webservers. The base configuration of a pterodactyl managed instance is an egg, which is basically a docker image wrapped in a bunch of configurations[1]. This means you can run any docker container in pterodactyl and manage it all through a fairly slick web panel[2] which allows you to easily tweak things like memory allocation, send commands directly to the console, and share access with other accounts. There's lots of eggs already configured for minecraft and other games like Rust (not the programming language), so a lot of the complexity of setting up a docker container is abstracted away and for a non-advanced user its a pretty nice balance between the ease of use for a realm and the extensibility of a full server.

[1] https://pterodactyl.io/community/config/eggs/creating_a_cust...

[2] https://streamable.com/hlscux (an example of a panel for a server I administer)