can I use ios 14 on ipad mini

That would depend upon your iPad mini...

• iPad mini4 or mini5 (current) - iPadOS 14.0.1
• iPad mini2 or mini3 - iOS 12.4.8
• iPad mini1 - iOS 9.3.5 (WiFi Only) or iOS 9.3.6 (WiFi+Cellular)

The tags appended to your post suggest that you have an original first generation iPad mini. Therefore, the answer is no, your iPad mini1 is not compatible with iPadOS 14.

The original iPad Mini cannot be updated beyond iOS 9.3.5 (or 9.3.6 if cellular).

The iPad Mini 2 and 3 cannot be updated beyond iOS 12.4.8.

The iPad Mini 4 can be updated to the current iOS 14.