Here is the full list of all 46 MXGP 2020 - there are The Official Motocross Videogame achievements.
Start replay at the end of a race in any game mode
Perform a Scrub in any game mode
Win a Grand Prix at Imola in any game mode
Purchase any bike for the first time
Make a purchase on the Rider Customisation page for the first time
Win a Grand Prix at Agueda in any game mode
Win a Grand Prix at Orlyonok in any game mode
Win a Grand Prix at Neuquen in any game mode
Get 10 Holeshots in any game mode
Win a Grand Prix at Pietramurata in any game mode
Complete a valid lap in Time Attack
Cover a total of 100 Km - 62,14 mi
Finish first in a race with the weather set to Rain in any game mode
Win a Grand Prix at Afyonkarahisar in any game mode
Win a Grand Prix at Kegums in any game mode
Win a Grand Prix at Valkenswaard in any game mode
Win a Grand Prix at Matterley Basin in any game mode
Win a race without falling and without using Rewind
Get a Holeshot and finish first in the same race
Complete a race without using Rewind
Complete a lap without falling on any track and in any game mode
Access Photo Mode for the first time in any game mode
Use Rewind for the first time in any game mode
Reach Prestige level 100
Achieve the podium 50 times in Grand Prix
Get a total of 300,000 MX Credits
Reach Prestige level 50
Reach Prestige level 75
Get a total of 200,000 MX Credits
Reach the first position in all sessions in a race set to a Full weekend
Win a race with physics level set to Advanced
Win a Grand Prix at Loket in any game mode
Win a Grand Prix at Teutschenthal in any game mode
Win a Grand Prix at Uddevalla in any game mode
Win a Grand Prix at Shanghai in any game mode
Cover a total of 500 km - 310.69 mi
Cover a total of 250 km - 155.34 mi
Get a total of 100,000 MX Credits
Reach Prestige level 25
Win a championship in Championship mode
Complete a race with race length set to Realistic
Win a race with AI Difficulty level set to Realistic
Cover 45 Km - 31,07 mi in Free Roaming in the Playground
Cover 15 Km - 6,21 mi in Free Roaming in the Playground
Save your bike's setup for the first time
Cover 30 km - 18.64 mi in Free Roaming in the Playground