is that okay to always plug and use the MacBook

Micromanaging your battery is not doing it any good. You'll get the best service and battery life by using the Apple supplied charger and letting the battery circuitry do battery management.

Not charging it to 100% and not allowing below 40% does not gain you anything.

I use the application AlDente whenever I am using my Macbook plugged for a longer time. It stops charging at a certain percentage (80% for example), and switches to using the power directly from the adapter. This should help prolong the battery health. I also practice the habit of keeping my battery in the range of 40-90%.

Hi,

Following article could help your question.

https://www.makeuseof.com/macbook-battery-health-plugged-in-charging-all-the-time/