29 inch wheel are the norm now, not much for 26 inch left. Although, continental still have good mtb tyres for 26 inch like the raceking, crossking, mountain king etc. I think Panaracer too. Wheels that 2.2 inch+ are common too for offroad. I use 2.2 inch race kings and they seem to be the best balance between speed, performance, and weight but I don't do any crazy trails, just some casual offroad like dirt, gravel, and roots in forests. The theory is that skinnier wheels are faster, which is technically true. But, over the years, it seems people have found wider and bigger tyres to be better because, although the raw speed on flats are lower, the ability to glide over most terrain more than makes up for it.
TPU inner tubes are getting popular too. I run them and it's instant -300 to 400 grams compared to standard butyl. Worth the upgrade. Lots of trail folks run tubeless but they require high pressure output to set up like a compressor. I still prefer tubes because ease of use.
Steel frames are still used by ye, they are harder to come by and usually only available through smaller companies that do custom made stuff.
I don't run clips (clipless, dumb name) so cannot comment on that.
As for your fork I don't know much about that one but air forks very popular now. Cheaper ones have only one side working, more expensive have both sides with suspension and dampers etc etc.
Tbh, older cranksets and shifters are still perfectly fine. I have a 16 yr old trek 3700 that I've modded to shit through aliexpress but the original gears and such are still there. V brakes are still cool too.
Honestly, your bike is still very capable. Bikes, at the core, haven't significantly changed that much over the years. If all your stuff works, then no real need to change.
With your MTB, I am not sure if there is much worth changing unless you want to splash big on new suspension. Maybe new tyres if current ones have worn out.
Your other option is to turn it into a lightweight gravel bike. I have done that with my trek 3700. It started off at 15kg, and I shaved it down to 10.8kg which made it significantly faster overall, and much nicer to carry around. Changing to a lightweight aluminiun or carbon fork will make a huge difference on its own. After that, you can change smaller things like installing TPU inner tube, carbon seat post, carbon saddle, lighter handlebar and stem. Then you could convert it to a 1x system where is only one chainring (called a "narrow wide") at the front meaning you cut out the front derailleur and shifter, shaving off more weight and making the bike simpler to maintain and use.
But I think you should just ride it first. Maybe ask someone to borrow their 29 inch wheel bike too because, as much as I hate to admit it, 29 inch wheels are just much more comfortable to ride.