Ah well. It doesn't matter.
They just don't want to implement it and they try to avoid this topic completely so it's unlikely that it will have background support like literally every other app.
Being slow is one thing and it wouldn't matter if there would be background sync.
The background sync is also necessary so that your mobile device is getting changes quickly when you change something on another client.
Otherwise you might change the same note and you'll automatically run into a conflict because you didn't let it finish completely after starting the mobile client yet you edit it and then Joplin just doesn't know what to do.
Laurent started out with weird lies like background sync
Cannot currently be fixed due a limitation of the underlying framework
or other lies like
we rely on existing libs, which for now don’t exist on React Native
and I tried to properly argue that the mentioned reasons are valid
After three years, one of the contributors summarized everything with reasonable arguments and even user reviews (you have to click to read that post because Laurent decided to hide it and to mark it as a "duplicate" (which doesn't make any sense either).
Laurent's response was just that he hid all the comments and locked the issue.
I am not aware of any note application without background sync except Joplin.
Anyway, I have high hops in Notesnook, they're already pretty neat but I'm waiting until they finished self hosting.
Their sync server is FOSS but they didn't publish an image on Docker Hub nor did they add any docs or added the server URL setting.
So all in all: try to live with Joplin not having a background sync or migrate to any other application.
People asked for this in 2018 so you should not expect Laurent to change his mind in 2024. 