Hi karam sawalha,
For glossy effect you need to inspect the element and adjust glossy effect as you want using second slider .
after that it generate a Hex code, then use this hex code for your container background color for glossy effect.
In your share picture container background color is white so first select container background color white after that adjust glossy effect using second slider .
so here the glossy effect background color code is
background-color : #ffffff66;

if you not find hexcode then use arrow down/up for change code to Hex code.

Demo link : https://personal-x1ixzlcz.outsystemscloud.com/PreviewInDevices/?IsMobilePreview=True&DeviceName=Smartphone&URL=/MyTasks/Screen1?_ts=637950854290201579
I'm also attach .oml file , please check it .
Thanks