Hi @Atul Kumar,
Thank you for posting in this community.
Sessions don't really time out if we are using Windows authentication which will re-validated automatically, and we could not set the session timeout.
You can refer to the answer in this link to get mor information about SharePoint 2019 idle time out. I hope it will be helpful to you.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.