As indicated in the documentation, you can input a straight glissando line with the popover by inputting gliss, or a wavy version of it with glisswavy.
Nevertheless, both ways produce a glissando line with a style property override, whichever the engraving default for this setting is, losing the advantage of getting the defaults you have already set for that project.
IMHO it would be great if inputting gliss would produce a default glissando line with no property overrides, while inputting glissstraight would create the straight version of it if you want the current behavior.
