Our org used Jira on-prem for 2k engineers and 3k additional staff and it was slow as molasses.

The dialogues and context menus took forever to show and page navigation was beyond painful.

We had dedicated engineering for maintaining our Jira and Bitbucket, and they still fell over. We eventually moved back to GitHub. (Our usage went from GitHub on-prem pre-MS -> Bitbucket on-prem -> GitHub cloud post-MS.)

I hate Jira regardless of where it's deployed. It's a beast.