You could create a list view from parent records then have a link icon to open a modal popup that shows the related line items. You can add rich text to the list view records to make it more attractive. I’m sure there is no end of customisation you could do with some CSS if you’re a coder. Not sure if I have understood your requirement but I have done the below with a a bit of code for the card borders.
(credit Johnny Parsons - Knack.mods - List Cards)
May be worth checking out Knack.mods:
https://forums.knack.com/t/even-more-tips-and-tricks-from-knack-mods-this-week/8473
#view_XXX .kn-list-item-container { /*change XXX to your view*/
border: solid 0.4px grey;
-webkit-box-shadow: -1px 2px 5px 7px rgba(163,163,163,0.33);
-moz-box-shadow: -1px 2px 5px 7px rgba(163,163,163,0.33);
box-shadow: -1px 2px 5px 7px rgba(163,163,163,0.33);
margin-top:20px;
padding-bottom:30px;
}
