I have just bought a DELL XPS 15 (7590) with ram 16GB, ssd nvme pcIe 512GB, Nvidia GTX 1650, CPU i7-9750H and 4K OLED display configuration. Before I had a HP 15-p013nl in the configuration with ram 12 GB, 1TB of ssd (originally it was a 1TB of hdd, then I updated it with a ssd), Nvidia 840M, CPU i7-4510U and a WLED display 1366x768 (it is an HD resolution, I think).
On both my pc's I run Project Cars 2. On both I found out the same problem: the game sometimes slow down at 0.5 speed and then restart at x2 speed recatching the time lost between the normal speed. So, for example, in fps, if I play at 60 fps, sometimes I slow down at 45 fps (also at 58-59 fps I see those problem) and then after some time I play at 75 fps, gaining the time lost and a average framerate of 60 fps.

Usually I play with the Nvidia reccomended setting. With the DELL they are:
- Antialias: FXXA medium;
- Car details: medium;
- Shadow details: no;
- Track details: medium;
- Texture filter: anisotropic 4x;
- Quote rendering frames: 2;
- Enviroment map: low;
- MSAA: no;
- Resolution: 2048x1152 (full screen);
- Texture resolution: medium;
- Advanced mirror: no;
- Oversampling: no;

The old one PC isn't anymore available, so I cannot find out the settings of it.
I have a pc stand with two fans on where I put the laptop while I'm playing.

To see some data, I installed MSI Afterburner and I noticed two things:
- The GPU, on this settings, is working at 40-50% at 70-80C. If I put a 3840x2160 resolution it go almost at 99%. On the other resolution it works almost ever at 40-50%.
- When the CPU reach the 40% of usage, the problems comes out. When I start the game the first time, the temperature reache almost 100C and the usage is 15% (on the 2K reccomended settings). The temperature then slowly drops down and then, when it reachs almost 80C, the usage of the CPU reach the 40% and the game start "lagging".
- If I start a race when I launch the first time the game, I can finish also a 24 hours race, but if I restart it after almost 30 minutes of playing, the problems comes after the first corner and I have to restart the PC to solve them.

I already tried to reinstall the game (both on internal ssd and external hdd), I tried to reinstall all the graphic cards drivers (I also have a Intel UHD graphics 630 on the DELL) and also a complete re-installation of Windows 10 (I have the Pro edition).

I already have sent these information to the BANDAI NAMCO support and they told me that is a BIOS problem, but, after I asked what precisely was the problem of the BIOS, they told me to ask on the forum and to look for a BIOS update. I look for it, but I already have the latest update of it...

I know that my laptop isn't a gaming one (I use it principally for work, but sometimes I want to get some fun), and in this way I'm also available at solutions that make me able to play at lowest setting and 15 fps, but I also tried those setting and the problems always comes out...
I also play with games like F1 2019, Assassin's Creed Odyssey, Assetto Corsa (yeah, I'm a traitor XD), but only on both Project Cars and Project Cars 2 I get those problems...

For other information, ask me!
Thank you for anyone tries to help me.

I looked for other treads with the same my problems, but I didn't found out anyone. Please link it if you see one.