Dell gaming monitor stuck at 60hz refresh rate with 2020 MacBook Air Intel i3

MacBook Air (Retina, 13-inch, 2020) - Technical Specifications - Apple Support

"Simultaneously supports full native resolution on the built-in display at millions of colors and: 

• One external 6K display with 6016-by-3384 resolution at 60Hz at millions of colors, or
• One external 5K display with 5120-by-2880 resolution at 60Hz at millions of colors, or
• Up to two external 4K displays with 4096-by-2304 resolution at 60Hz at millions of colors"

Use an external display with your MacBook Air - Apple Support indicates that the primary external display on a M3 MacBook Air can have a refresh rate of 144 Hz, if the display has a resolution of 4K or less. But the 13" and 15" M3 MacBook Airs are different, newer models.