If the system processes a request longer than for 2 seconds, it’s essential to illustrate users that the website is working on it. In other case, users may leave the website.

Loaders shouldn't be too sophisticated:

https://s3-us-west-2.amazonaws.com/secure.notion-static.com/588e7c11-e328-4f74-93c4-cbd11589c67d/Screen_Recording_2021-01-02_at_1.01.26_PM.mov