When an SD card is inserted into a computer running Linux Mint the card is automatically mounted and an icon is displayed on the desktop. Using this icon you can view and modify files. It also would appear that you could format the card as well by right-clicking on the icon.
When the option to Format is selected a dialog box to format the card is displayed but, the button to Format is not clickable:
The trick is to use the Disks utility to format the partition on the card. First, open the Disks utility:
Next, select the SD card on the left then click the gear icon under the partition on the SD card:
Then select Format… from the context menu:
Now a dialog box is displayed with the Format button enabled. Provide a name then click the button Format:
The next window is confirming your actions. Click Format to begin formatting the partition on the card:
Note: if you click the single gear icon at the top-right corner (near the SD card’s name) the same dialog box will be displayed. It will appear to format the card but, it doesn’t. You have to format the partition on the card.