Here is the full list of all 50 MXGP 2019 - there are The Official Motocross Videogame achievements.
Reach Prestige Level 100
Complete all The Final Showdown challenges within the Playground
Validate 5 Custom Tracks
Complete all Speed Trial challenges within the Playground
Sign a contract with the Rockstar Energy Husqvarna Factory Racing MXGP team in Season mode
Sign a contract with the Team HRC MXGP team in Season mode
Sign a contract with the Red Bull KTM Factory Racing MXGP team in Season mode
Complete a Championship in Season without changing Official Team
Sign a contract with the Monster Energy Kawasaki Racing Team MXGP team in Season mode
Win the MXGP Championship in Season mode
Race a total of 408 km (253,4 miles)
Sign a contract with the Monster Energy Yamaha Factory MXGP MXGP team in Season mode
Win the MX2 Championship in Season mode
Win a Grand Prix at Shanghai in any race mode
Win a Grand Prix at Afyonkarahisar in any race mode
Take the podium 50 times in Grand Prix or Season mode
Win a Grand Prix at Uddevalla in any race mode
Reach first place in all sessions in a race set at Full Weekend
Win a Championship in Championship mode
Complete a Grand Prix in a Custom Track created by another player
Finish first in a race under Rain in any race mode
Win a Grand Prix at Imola in any race mode
Beat another player's Ghost in Time Attack mode
Race 25 Km in free lap in the Playground
Win a Grand Prix at Lommel in any race mode
Win a Grand Prix at Loket in any race mode
Win a Grand Prix at Semarang in any race mode
Replace all Stock Components in the Season preset of your Sponsor bike
Win a Grand Prix at Teutschenthal in any race mode
Win a Grand Prix at Kegums in any race mode
Win a Grand Prix at Orlyonok in any race mode
Validate 5 Waypoint Paths
Complete all Dexterity Trial challenges within the Playground
Win a Grand Prix at Saint Jean d'Angely in any race mode
Win a Grand Prix at Agueda in any race mode
Compete on a Waypoint Path created by another player
Complete all Gathering Trial challenges within the Playground
Win a Grand Prix at Mantova in any race mode
Win a Grand Prix at Pietramurata in any race mode
Win a Grand Prix at Valkenswaard in any race mode
Start the replay at the end of a race in any game mode
Save a Bike Setup for the first time
Sign your first contract with an Official Team in Season mode
Win a Grand Prix at Matterley Basin in any race mode
Win a race with the physics level set to advanced.
Win a Grand Prix at Neuquen in any race mode
Complete a race using the Helmet Camera in any game mode
Use the Rewind for the first time in any game mode
Get a Holeshot in any game mode
Sign your first contract with a Sponsor in Season mode