The main reason why your printer is offline is because it is not set as the default printing device. Navigate to settings and go to printers and scanners. Then, click on printer and from the list of printers select your printer as the default printing device. Let’s see how do I change print status from offline to online. Under the devices section in your computer check, if it is listed as devices. You must re install the driver from the website. In case, you need to use the Brother Printer offline. Right click on the icon of Brother Printer machine. Then, see what’s printing and change it to online.

Source:-https://telegra.ph/How-to-Fix-Printer-Offline-Issue-04-05