Jenkins plugins

what is the official website to download plugin.txt for jenkins

What should be in this file?
The update center provides some json files that describe which are the latest plugin versions and their dependencies to other plugins

I’m a beginner and I want to update Jenkins as :
docker cp /your/path/to/plugins.txt <container_name>:/tmp/plugins.txt
docker exec -it <container_name> /bin/bash
jenkins-plugin-cli --plugin-file /tmp/plugins.txt --plugins delivery-pipeline-plugin:1.3.2 deployit-plugin
cp -r -p /usr/share/jenkins/ref/plugins/. /var/jenkins_home/plugins/.

you have to write that file yourself. It contains the plugins that you want to install. Only you know which plugins you need.

do we specify the version?

You can specify the version if you want.
see GitHub - jenkinsci/plugin-installation-manager-tool: Plugin Manager CLI tool for Jenkins