EDIT 4/21/21: Niantic has tweeted the following:
Pokemon Go will have their Friendship event Saturday, April 24th 11am – 2pm local time. The following will be happening during the event!
- Grass Pokemon appearing more frequently
- 3x Catch XP during the event
- Incense and Lures started AFTER the event has begun will last three hours!
- A Collection Challenge will reward 100,000 XP once completed
- A Global Challenge event will take place during the event with a total of 20K Exp possible to earn for individuals
- Green confetti will appear on the overworld map
On Saturday, April 24th 11am – 5pm trade distance will be increased to 40km with increased chance of Lucky Trades
You can find more information at https://pokemongolive.com/post/friendshipday-grass-2021/?hl=en