I have a Lenovo Yoga 920 laptop with UHD Graphics 620 and a new wide 3440x1440 monitor. The max resolution that i can achieve is 1920x1080. Using a DP connection and drivers are up to date
First of all, make sure that the USB-C-to-DP adapter/cable that you are using is compliant with the Thunderbolt 3 specification.
Secondly, remember that poor quality cables can limit data throughput and could even prevent the monitor from going to higher resolutions and could prevent the system from reading its EDID data.
Third, check if the display manufacturer provides a download for an update (.INF) file that provides information on the modes supported. Some manufacturers refer to these updates as "Drivers".
Hope this helps,