Microsoft Flight Simulator

This achievement takes about 6-10 minutes to complete. For visual learners, here is a video guide for the Windows 10 version that I used to get this achievement on Xbox Series X. Note that this is not my video:
For those who prefer text instructions, here are the steps to take:
Turning Off Assistance
1. From the home screen, use RB to navigate over to Options and select it with the A button.
2. Select Assistance and then change the difficulty level to "True to Life". This should automatically switch every sub-option below to Hard.
3. After that, save the settings by hitting the Y button, and then press B to go back to the home screen.
4. Use LB to navigate back to the Welcome tab and select World Map.

Choosing the Plane and Airport
1. In the top left corner is an icon of an airplane. Select it and then either navigate manually over to the Airbus A320neo or search for it and select it. Don't change any of the other options (e.g. liveries, etc.)
2. In the From section, select a departure airport or search for one using the search bar. I used SBGR.
3. Still in the From section, choose a starting point that isn't a runway, such as a gate. I chose Gate(Gate 11 - Gate Medium).
4. You can leave the To section blank and just click the yellow Fly button in the bottom right corner.

Before Starting Engine
1. You should now be in the cockpit. There should be an open help box to the left called Checklist. If there isn't, click LS on your controller to bring up the top menu and use LS to navigate the cursor up to it, selecting the checkmark with the A button to bring up the Checklist. You can close any other boxes that may be open by navigating to the 'x' on them and using A to close it.
2. In the Checklist, there are three sections: Before Starting the Engine, Starting the Engine, and After Starting the Engine. Begin with Before Starting the Engine. You can navigate them with a combination of the LS and RS.
3. There are 11 tasks you must complete under "Before Starting Engine". Start with the one on the top and work your way down. It's important to do them in order. You can see a list of tasks to the left (e.g. Battery Switches, External power, etc.), followed by a status for each one (e.g. On, On if available, etc.). Move the LS over "Battery switches" and press the A button to highlight it.
4. Once highlighted, more information will be provided on the bottom of the box, below "Tick Item" on how to complete the task. Selecting "Battery switches", for instance, will offer the following clue: "Battery switches must be set to ON". To do this, use LS to move the cursor back up to the Battery switches row and, towards the right side will be an eye icon. Select it with the A button and the camera will jump you towards to appropriate button or instrument in the cockpit, where you can then follow the on-screen button prompts to turn it on or off, as needed.
5. Confirm that the status of the Battery switch button is set to ON in the cockpit, and then move your cursor back to the Checklist box and select Tick Item to mark it as complete and have it automatically move down to the next one: External power.
6. Continue through the next four tasks in the checklist--External Power, Engine generators, Engine bleed air switch, APU master switch, and APU start--by selecting the next task, reading the description, using the eye icon to move the camera over to it, and adjusting it as needed, and then selecting Tick Item.
7. Important Step: After you complete APU start by turning it On, note that the next task is also for APU start but, this time, to wait for the APU button light to switch from displaying "ON" to displaying "AVAIL". You must wait for this to happen before proceeding. It takes about 28 seconds. Once it does, select Tick Item back in the checklist.
8. Following that, proceed normally by completing the remaining tasks--APU bleed, External power, Fuel pumps, and Beacon--as described and selecting Tick Item when complete.

Starting Engine
1. Once all 11 tasks under Before Starting Engine are complete, move the cursor to the top of the checklist box and select Starting Engine. There are 5 tasks to complete. As before, do them in order, top to bottom.
2. Important Step: Starting with Thrust levers, they need to be "Idle", which, for me, they already were. I mistakenly thought I needed to move them forward but that was not the case. So just leave them be and click Tick Item to move to the next task.
3. Turn the Engine mode selector to IGN/Start and tick the item off, then turn the Engine master 2 switch to On and tick the item off, and then turn the Engine master 1 switch to On and tick the item off.
4. For me, that was the last step I needed to do, as now the engines should be stabilizing on their own. After ticking off the Engine Master 1 switch task, the achievement should pop in about 30 seconds to 1 minute. In the meantime, you can click on the eye of the next step, "Engines (confirm stabilized)" to watch in real time as they begin to stabilize. If the achievement doesn't pop after a minute, try ticking the Tick Item box for that task and then proceeding on to the final three tasks in the final section at the top: After Starting Engine. It should definitely pop after that.

Start any free flight with the Airbus A320neo at any airport. Make sure you start at a parking stall or gate in the dropdown under the airport you choose.

The aircraft will be cold and dark. The checklist will walk you through starting the plane up and does not count as using Assistance.

Once you start any engine, left or right, achievement will unlock.