A recently released SF book has single neutron star on the veritable edge of collapsing into a black hole...
"What's going on with the star?"
"It's massive. I mean, like, spit-on-it-and-it'll-start-to-collapse-into-a-black-hole-level massive"
"More than three stellar masses stuffed into a ball half the size of Rhode Island," Jen said.
"But when a rapidly spinning neutron star collapses into a black hole, a gamma ray burst comes out of the poles. A few seconds of it releases a much energy as Sol would in its whole ten billion years"
...collapse into a black hole. (Actually on looking back, there's nothing that says it did collapse, just evidence of something very energetic)
I know that a giant star collapsing (directly into a black hole or neutron star) will shine rather brightly, as well as pairs of merging neutron stars (e.g. GW170817), but if there's just a single neutron star (or quark star) that gradually becomes large enough to where it gets swallowed by an event horizon, would that be that dramatic?
Some brief amateur research turned up things like Quark-nova, a speculated phase transition of a neutron star that could release nova-level energy rapidly. Are there any other catastrophes that are known or speculated to happen to a lonesome neutron star?