Welcome back! While we've before, I definitely recognize your name from the occasional historic browse through old wiki articles and forum posts, so it's for sure pleasant to see someone from so long ago return. I only joined the wider community in 2019, but I'll do my best to point you around...
Regarding SRB2 itself, it's received 3 major updates since v1.09.4 - v2.0, v2.1, and v2.2, with the former two adding all sorts of new modding features as well as many new zones to the campaign and the latter coming out in late 2019 and giving the game the professional polish you've noticed. It's an understatement to say v2.2 was a huge leap in quality for the game and community.
Speaking of community, the most major shift happened around 2017-2018 when the IRC chatroom declined in popularity and moved to
a Discord server, which is where most community members reside today. If you're looking to reconnect with any potential old pals, the best option would be to poke around there if you haven't already. Besides that, there's active daily discussion of the game itself and all the modding that goes on. OLDCs are still held regularly, with many entries from both experienced and inexperienced authors. The game is also partially developed through
the public GitLab, which allows community source code contributions for minor patches.
And modding! For sure, it's received a huge overhaul from the days of Final Demo. The Lua scripting language is now supported as of v2.1 (2014), which has led to incredibly complex game-changing scripts being developed over the years. Lua scripting and general mod editing takes place in the advanced lump editor
SLADE now, rather than... I believe XWE? SLADE is overall much more stable than XWE and supports many modding features (such as Lua syntax and .pk3 file formats).
Regarding mapping, many new features have been added to SRB2 itself such as slopes, PolyObjects (moving geometry), flat alignment, and flats/textures being interchangeable now. SRB2 Doom Builder has also long been dethroned as "the SRB2 mapping tool" - since 2016, a fork of the much more developed GZDoom Builder (aptly titled
Zone Builder, as I'm sure you heard earlier in the thread) has been the go-to mapping program, with support for all of SRB2's features (such as slopes, flat alignment, custom objects, and Lua scripting in-editor just to name a few).
Generally, a lot as changed since Final Demo so I suggest you take a look around. Once you finish the main game, I highly recommend you take a look around the Addons forums and play around with what the community has to offer. Sorry for the textwall, but this should be everything you need to know about how things go around here nowadays!
edit: silly me, didn't realize this thread is almost two months old when posting this. All of this information is still relevant, however, if you haven't looked into it since then.