Festuca perennis/ Lolium multiflorum

I`d second the Lolium mutliflorum, I think the seed heads are pretty characteristic.

and the leaf blades tend to be very shiny on the underside

could the linked pic be from an old Elymus repens? I have a dim memory of their seeds sitting in a different angle at the middle axis and thus creating that zig-zag look

There are no recorded observations of Elymus repens in Dallas, Texas, USA, but several observations for Lolium multiflorum. ID confirmed by Texas botanist Aidan Campos.

https://www.inaturalist.org/users/1739755

It's very interesting how similar Elymus repens and Lolium multiflorum are.