Yes, you can sign in from multiple devices with a single account.
The number of the devices is as follows:
One from “desktop (browser)”
One from “desktop (desktop app)”
One from “smartphone”
One from “tablet”
For instance, you can simultaneously sign in from a “desktop(browser)”, “desktop(desktop app)”, “smartphone” and “tablet”.
However, you cannot sign in simultaneously from “iPhone” and “Android smartphone”.