Events/News as a section in the main menu are pretty much a must to activate the playerbase and encourage UGC.
The best system I had seen so far would come from clash of clans in terms of the structuring. An event menu that opens up to 4 sections;
News: Info on updates, patch notes, highlighting new units/assets, information on big changes in other variants, basically, regular and special special events like anniversaries, tournaments or contests…
Also a place to visibly add buttons that link to the game and variants discord/yt/ig/fb/forum
Events: In-game/Out-game Events, in-game events that limit their actions within the game like:
Week of Cloak and Dagger: Kill 100 Units with an Assassin, Lasiq Assassin or Spy in multiplayer matches.
Progress 15/100
01.07-08.07 / 3Days2Hours remaining
Rewards: Limited Event Skin x for Assassins.
Matchmaker Madness: Create and finish 10 multiplayer matches.
Progress: 3/10
01.07-31.07 / 17Days 3Hours remaining
Rewards: 25gems & limited matchmaker madness loading screen.
Obviously those are just basic examples but this way you can easily create interesting and engaging events that draw your players in and give content creators the possibility to create interesting material. By having both direct in-game event options: kill x, heal x, build x, train x; you can motivate players to try other game styles that meta usually prohibits, this giving change to players. Mechanic in-game events like: create&finish x multiplayer matches or adding certain event only micro campaigns can help you keep certain game modes more active and steer player movement.
Out-Game Events would include anything that at least partially happen externally like fan art contests, map creation contests, unit design contests and alike, these events are true driver’s within the community and would either be rewarded with very special and unique to the winner cosmetic item and maybe even cash prices.
These are usually best made with a voting/poll system in which the community decides in multiple rounds between all the entries, each participant only getting one entry per such event.