Hello Dave,
On the Debian Bookworm systems here using stopport releases the associated device regardless of whether it is a h/w or virtual serial port or even a network port to a s/w tnc. I am able to temporarily use the device for something else and when finished easily "reactivate" it in linbpq using startport.
I assume most linux variants will behave the same.
73 de Rich WA3WLH
David VK2NA