Version of OpenTTD

12.0 release

Expected result

When setting the game in VSync, it has to be smoother as it synchronize the game refresh rate to my monitor refresh rate

Also to note:
1x game speed has to look smooth without other extra things to do but 2x game speed is really far smoother either in vsync mode or non-vsync (And it's the case even when a vehicle goes 0.5x it's speed to match real 1x speed; it looks so much smoother when moving).

Actual result

[This has been seen after a lot of testing and fine tuning with my monitor]
---with vsync-on---
When moving on the map -> it feels really smooth compared to non-vsync
When vehicles are moving -> they feel more laggy like it cut frames out compared to non-vsync.
2x game speed look far smoother than 1x game speed.

---with vsync-off---
-> Vehicles moving look much smoother.
-> Moving around the map looks laggy compared to vsync-on.

Update
////// The bug targeting VSync-only DOES NOT Happen when not in Fullscreen //////

Steps to reproduce

[Example with 75Hz refresh rate monitor]
1- Set vsync-on
2 - see that fps never goes to 75fps like it has too (it stays at ~67-68fps) and so makes some things laggy
3 - The game itself will look smoother but the vehicles will look like some frames are cut.
3 - Set vsync-off
3 - The game itself will look laggy but the vehicles will look smoother.