Drive 3B
After the first fight in the first area you can go right to the next area. Ignore that and go left to find the Back Door. Defeat all 20 enemies.

Drive 5B
After opening the locked barrier with a key, go left to find the Back Door. Break the boxes to find the key and unlock the barrier to get out within 3 minutes. The key is located in one of the two barrels behind you.

Drive 8A
In the second area after the Keeper, ignore the stairs. Instead follow the path to the right, go around the corner, and a small door on the right will be open. Go inside this classroom to find the Back Door. Keep the enemy in the air for 10 seconds.

Drive 10A
After the third Fragment, ignore the mission marker and go the opposite way. At the far end of that path is the Back Door. Find and destroy all 3 Lady Stones in the area before your HP runs out. Attack enemies to gain health. You can also use potions to restore health.

Drive 12C
After the first fight in the third area (the cave with the blue crystals), turn left and follow the path. Mow all the large grass within the time limit.

Drive 15C
At the start of the first area, defeat the enemies, the look at the left side of the area for a small path that takes you behind the giant sprocket. Mow all the large grass within the time limit. There a lot more grass this time, but you also have more time. Having the Final Drive unlocked will make this very easy.

Drive 16B
After the first fight in the first area, ignore the mission marker on the right and go straight ahead. The Back Door is at the end of this path. Find and destroy all 4 Lady Stones in the area before time runs out. All the Lady Stones are around your starting location.

Chaos 17B
After making it to the second area, ignore the mission marker at the top of the stairs and go down to another area. Keep fighting enemies and you'll get the key. Afterwards go back to the mission marker, head to the next area, defeat the enemies, then ignore the mission marker again, and go the other way. Unlock the barrier with the key to access the mission. Survive for 3 minutes while your health is constantly being drained out and recover health by defeating enemies or by using potions. Using Manpukumaru as an Extar and having her Final Drive will be a huge help, as she has the highest attack boost of all Extars.

Chaos 18A
Immediately at the start of the fourth area take the path to the left. Keep the enemy in the air for 30 seconds while your health is slowly being drained. Just use the combo from the secret mission in Drive 8A to clear it.

Order 18A
In the second area after the first fight, ignore the mission marker on the left and go right. The Back Door is behind a breakable barrier. Pass through all 10 checkpoints within 40 seconds.

Order 19B
In the first area ignore the mission marker on the teleporter and take the path behind the houses. Defeat all 27 enemies. You can take it easy as there's no time limit or health drain.

I was running across these two problems for the longest and just wanted to share what I personally did to fix my issue in case anyone is struggling as well. 🐾 🐈‍⬛
🌸 1. Open the NVIDIA control panel
🤍 2. Navigate to 3D settings > Manage 3D settings
🌸 3. Open the Program settings
🤍 4. Select Preferred graphics processor for this program from the second dropdown menu. Your NVIDIA GPU should appear as "High-performance NVIDIA processor"
I hope this will help someone in the future that couldn't get past the C++ part at the end without encountering an error message. ʕ♡˙ᴥ˙♡ʔ