I logged into one of my Jira Cloud instance to realise that I can enable the new interface which looks like Jira Server version. It was actually the case for many years but couple of years Atlassian changed the interface with sidebars on the left. People complained a lot and they didn't like the new interface. Especially those who were using Jira for years.
I think Atlassian listened to the feedback and took this really seriously and decided to bring back the old interface. It is not exactly the same but you won't miss Jira Server now.
I made a video on this topic if if you want to take a look: https://youtu.be/UZcGwty_uac