I’ve seen a few sites get upgraded with 18.04, but most of them haven’t.
I’ve seen people manage to do a dist-upgrade, but it’s success is uncertain, and do you really want remnants of your 6 year old OS potentially causing issues for the next 5 years that 24.04 is supported? Also, an upgrade of 18.04 gets you only to 20.04, which is good for about another 60 days, so you’d need to run 3 dist-upgrades to get to the latest OS.