As per Plausible Documentation, custom events affect the bounce rate calculation, however it is possible to exclude them, by passing an interactive property:
To keep accuracy higher, you can optionally select which custom events you want to exclude from the bounce rate calculation too. To do that, mark any such events as "non-interactive" as explained here. These events are tracked but do not affect the bounce rate.
And further:
interactive - whether to include the event in bounce rate calculations (defaults to true).
To mark an event as non-interactive, you can set the interactive argument to false. This will exclude the event from bounce rate calculations. plausible('Custom Event', {interactive: false})
Currently, this doesn't seem to be supported by useTrackEvent.