Hi there!
Thanks for contacting us.
Is it the first slider?
If yes, then please use the following code in your custom CSS:
@media (max-width: 767px){
.main-slidshow.sppb-addon-sp-slider .sp-item .sp-background::after {
background: none;
}
}
Note: Path towards custom CSS(Joomla 4): System>Site Templates Styles> Click on your current default template name then choose Template Options. Then find custom CSS within the custom code.
https://prnt.sc/5mBuSRh907N3
https://prnt.sc/ooiq-lkMEXr_
https://prnt.sc/nunlX-f5AhK1
Best Regards