Need help deciding a class! (Returning player with lots of questions)

So the last time i played this game was before heart of thorns released, so its been a long time, i used to play a mesmer back then. I know classes are a lot different now so im not sure what to play, I play mainly mages in MMOs in general (mage in wow, black mage in FFXIV, sorcerer in ESO, sith inquisitor in SWTOR), so im torn between mesmer and elementalist, but since classes in this game are a bit more complex i have a few questions (i play mostly PVE)

What are fractals and whats the difference between them and dungeons and raids?

ive been reading classes work different depending on the content youre playing (chrono or mirage for mesmer), i couldnt really undertand what these mean or how it works

I know gw2 doesnt have the typical tank/dps/healer roles, but i know some can tank and support depending on how you build them, how do elementalist and mesmer work around this?

as i said im torn between mesmer and elementalist, how do these two play nowadays?

Please excuse my english! T.T

Dungeons are dead 5 man content , and 10 man raids likely as well (as in no further development has been announced) with the so-called ramp-up replacement being 10 man strike missions.

The majority of raids are centered around a boss fight unlike dungeons which are more story driven and 5 man. Due to the team composition demands and the damage enrage timers it's far less likely to be PUGed off LFG.

Fractals are 5 man content similar to dungeons with 4 tiers. Each tier has an additional "instability" which is an effect that makes it more difficult , as well as more health/toughness for the enemies. i.e. Tier 1 = no instabilities , Tier 2 = 1 instability , Tier 3 = 2 instabilities , Tier 4 = 3 instabilities.

For fractals , power weaver elementalist is considered "meta" and power chronomancer is no longer meta because of the ramp time of mesmer shatter mechanics and the prevalance of firebrands (guardians) for quickness & oftentimes healing as well. Neither weaver or power chrono are considered easy to play well , power tempest (elementalist) might be a superior option for more casual groups.

There's a new fractal coming on September 15 and LFG tool is almost always populated around reset time, so it's safe to say fractals aren't dead at all.

This really helps! Thank you!

I would add that dungeons are dead in the sense that not only are they not being developed or improved, for the most part nobody really plays them much (though you can still find groups if you really want to see them). Raid may be dead in the "they're not currently creating any new ones" sense, they're still very much alive within the community and would be worth getting into if that's your thing. They also still give very good rewards (which is probably at least part of the reason they're still active).

Fractals are the replacement for dungeons, are very active, and are definitely worth doing.

If you want to look into what classes/builds are in the current meta, I'd suggest looking at snowcrows for raids, discretize for fractals, and metabattle for anything else.