Welcome back. I'm surprised that nobody has yet suggested Modern Perl as a great resource for how to do things "these days" in Perl (even if "these days" is now a decade ago). I'd also recommend a quick browse through Task::Kensho for an opinionated but valuable set of go-to modules.

Frameworks for web development: what are the most popular ones?

For "the marketplace" you'll be unlikely to have to look further than Dancer2, Mojolicious and/or Catalyst.

Changes to the language itself

There's been a few syntax tweaks, a few behavioural changes and some importing of features from popular modules into the core. Nothing to get too worked up about, IMHO.

OO Perl?

Again, have a look at Modern Perl for a fair introduction. For "the marketplace" you will want Moose and probably Moo, but there are plenty of others. I'm a minimalist at heart so will happily give a vote to Class::Tiny if that's all you need.