Our beds are raised so is strim up to the edge no problem.
I now do my in law’s and their beds are lower so I scalp the edges if the mower wheels drop off the edge.
What can I use to cut the edges ? Imagine cutting grass on a kerb if you will.

Strimmer turned on it’s edge.
Most will have a rotating head or supporting wheel type arrangement to facilitate this?

Hold the mower roughly level with the outside wheels in the air?

That’s what I try to do yak ,not always with success. They also have a strip of grass 8 inches wide by 20 feet which is a pain.

Mower with a roller at the back FTW.

Then edging shears for a nice tidy finish. We have a strimmer, I can’t remember the last time it was used.

?