If you need to, you can use ESM with either Pro or Advantage. I think they're calling it Pro now. That'll net you another 5 years of security updates for some components.
ubuntu.com
It's time to consider your options if you're still using 18.04 on anything important or, especially, facing the public web.

Time to prepare for Ubuntu 18.04 LTS End of Standard Support on 31 May 2023 | Ubuntu
Ubuntu 18.04 LTS ‘Bionic Beaver‘, one of the most popular Ubuntu releases, will reach the end of the standard, five-year maintenance window for Long-Term Support (LTS) releases on 31 May 2023. What is an Ubuntu LTS release? Ubuntu LTS releases provide a stable, enterprise platform for...

It's time to consider your options if you're still using 18.04 on anything important or, especially, facing the public web.