The underlying triangle here: Out of time, scope, and quality, you can pick two to specify but you can't constrain all three.

Scrum specifies fixed time and quality ("definition of done"), with scope as the flexible variable, as tasks get pushed out of each sprint.

Kanban specifies fixed scope and quality, letting time be the floating factor for each task.

Waterfall specifies fixed time and scope, with the inevitable result that quality has to give way.

There are some applications that Scrum does fit better than Kanban, notably anything tied to a real world calendar, say a scheduled live event or a school year or holiday or other seasonal concern. But yes, most businesses don't need to be time-boxed with Scrum anywhere near as much as they think they do, particularly given how much of that time is always consumed by organizational friction around the time-boxing negotiations.

(What happens if you do try to constrain and specify all three? We call that a death march. Actually, time invisibly flexes as workers cram in effort at a higher pace, until they burn out and then you're back to quality implicitly or time explicitly giving way unless you reduce scope.)