The elongated seat on my Glacier Bay toilet cannot be tightened so that it stays in place for two days. I have contacted both GB and Home Depot but continue to struggle with a problem for another year.

Well, new toilet seats aren't that expensive. The big problem is that they use plastic bolts that, under tension, "creep" and therefore loosen.
https://www.bing.com/search?q=plastic+creep+explained&FORM=QSRE6

Kohler and TOTO toilet seats come with soft plastic washer that goes between the seat bracket and toilet bowl. These washers prevent seat from sliding sideways

Hope that helps

Milo

You also may want to ask other people living with you if they SIT on the toilet or FLOP onto it... I know that sounds crazy but I have a friend who ALWAYS flops down on her toilet. When I stay there I tighten the seat bolt and the seat stays put no problem as long as she is not in town and I am there alone. The minute she comes back she flops down and obviously falls to one side and pushes the seat with her. IT DRIVES ME CRAZY. But it is her toilet, so I have zero control over that.

Maybe a Rubber Washer on top and bottom. Help plastic bolt from loosening? I would clean and dry contact surfaces.