It's complicated, and the law leaves a lot of wiggle room. In principle, it can be a valid reason to end an employment relationship from the employer side if so

It's complicated, and the law leaves a lot of wiggle room. In principle, it can be a valid reason to end an employment relationship from the employer side if someone is unable to perform their work due to being in jail. However there's a lot of hoops to jump through for the employer - the absence has to be of "significant length", the employer has to be able to show they deeply looked into it when they came to this conclusion, they need to consult with the employee on it, they may have to look into alternative solutions to fill the gap, etc. As a guideline, if the absence is expected to be two years or longer, much of this is no longer expected by the employer. I think most employers would not get away with firing someone in this case.