Worked on a project with an old (12+ years?) - but still being developed/used - Java system. Just last year a move was made up to Java 11 (from 8). Decent test coverage, but moving multiple systems is still a big task, but... they did it. Java 11. Yay.
But... teammates were running in to issues with 'new' stuff - like, using 'var'. There were others, but this was sort of the archetypal argument. "Well, it doesn't match the rest of the style of the file/app - it'll make it hard to read". Well... hrm... any new feature literally doesn't match the style of what came before it, because you have new keywords/features/syntax to handle processes a new way. It's definitional. But just because there's a new feature doesn't mean it'll be adopted (for better or worse, I supposed, depending on your stance).
Java-the-language/JVM has picked up pace hugely in the last few years, but Java-the-ecosystem tends to lag quite severely. Not least because these systems tend to be entrenched systems that move quite a lot of money around... or are highly business critical in some other way. This leads to extreme conservatism wrt. upgrades, etc.
(That part has also gotten better, but especially the Java 8 -> anything later upgrade has been extremely painful because of modularization. Past Java 9 it usually isn't that much of an issue. However, JDK 11 was the first LTS release after 8, so most shops basically delayed the transition until JDK 11.)
