MacBook Air 2020 does not support 100hz display?
According to MacTracker (fan, not affiliated) the Macbook Air (retina, 13inch, 2018) supports:


  One external display with 5120 by 2880 resolution at up to 60 Hz, Up to two external displays with 4096 by 2304 resolution at up to 60 Hz


The 2020 air is as follows:


  One external 6K display with 6016 by 3384 resolution at 60 Hz, one external 5K display with 5120 by 2880 resolution at 60 Hz, up to two external 4K displays with 4096 by 2304 resolution at up to 60 Hz


So not 100Hz.