Dell S3422dwg resolution on MacBook Pro not showing resolution higher than 1920x 1080

I see that this is a 3440x1440 pixel widescreen monitor with both DisplayPort and HDMI inputs.

https://www.dell.com/en-us/shop/dell-34-curved-gaming-monitor-s3422dwg/apd/210-azep/monitors-monitor-accessories

How are you connecting it to the M2 Max MacBook Pro? WIth a HDMI cable, or with a USB-C to DisplayPort cable? If you are using a HDMI cable, is it the one that came with the monitor, or another high-quality HDMI cable? HDMI cables are not all alike, and the original/lower-spec ones were for 720p and 1080i HDTVs.

I had this problem too, and solved it by using a different USB C dongle - the small device you have to buy to get an HDMI jack on your macbook (for many models). Some of those dongles don't support 60Hz video. When I switched to a better dongle, everything worked! You can look for dongles that support 4K and 60Hz video.