Which one to go for?

@WallFlower26  I'm not surprised the MSI is sold out; that was a really good deal for the hardware.

You have a couple of options here.  One is you buy a laptop with 8 GB RAM and then have a computer shop upgrade it.  This is an easy upgrade to do, it shouldn't be too expensive, and it doesn't void the warranty.  Then you can choose from among the options that have the other features you want.  These would be examples with otherwise the same hardware as the MSI (except for the hard drive in the second one):

https://www.amazon.co.uk/Dell-15-6-inch-Anti-Glare-Gaming-Laptop/dp/B07TS97JKR/

https://www.overclockers.co.uk/hp-pavilion-15-dk0026na-nvidia-gtx-1660ti-8gb-15.6-fhd-ips-intel-i7-9750h-gaming-laptop-lt-04k-hp.html

This has a slower processor (still very good though) and is £100 cheaper:

https://www.box.co.uk/9S7-16W112-010-MSI-GF65-Thin-9SD-010UK_2737195.html

You could pay more for a model with 16 GB out of the box.  This one is £1,100, has a weaker processor, and is somewhat back-ordered:

https://www.amazon.co.uk/ASUS-i5-9300H-GeForce-Graphics-NumberPad/dp/B07TPNJG8S/

Or you could configure a Cyberpower laptop with 16 GB RAM and the hard drive size and type of your choice.  When this model is tweaked to have an Nvidia 1660 ti, 16 GB memory and a very fast 512 GB SSD, it costs £1,113.  (With a 1650 instead, it costs £965.)

https://www.cyberpowersystem.co.uk/system/Tracer-III-17-Turbo-100-Configurator

The version of the above with a 15" screen costs £1,124 with the same hardware:

https://www.cyberpowersystem.co.uk/system/Tracer-III-15-Slim-Configurator

So you need to decide how you want to approach this, and then it will be easy to find the best option.

@puzzlezaddict what is there equivalent to the MSI?

@WallFlower26  I meant that the hardware was equivalent to the hardware in the MSI.  But really, if you're willing to spend over £1,000, you can get what you want.  Decide what that is, and I will point you towards a couple of good options.

I’d like a laptop that has 18 GB, equivalent specs to the MSI that’s sold out.

@WallFlower26  There are two other MSIs with the same specs at Overclockers, both for £1,200.  The only difference is the screen size: 15" vs. 17":

https://www.overclockers.co.uk/msi-gl65-nvidia-gtx-1660-ti-16gb-15.6-120hz-fhd-i7-9750h-gaming-laptop-lt-2ae-ms.html

https://www.overclockers.co.uk/msi-gf75-nvidia-gtx-1660-ti-16gb-17.3-120hz-fhd-i7-9750h-gaming-laptop-lt-2ad-ms.html

You could get the 15" version for £1,127 from a third-party seller on Amazon:

https://www.amazon.co.uk/MSI-Gaming-9SD-478UK-Notebook-i7-9750H/dp/B07RT1Z55R/

Or you could get a custom built PC with the same hardware.  Cyberpower's 15" (slim) and 17" models are £1,147 and £1,136, respectively.

http://www.cyberpowersystem.co.uk/saved/1940982

http://www.cyberpowersystem.co.uk/saved/1940985

You could also get this one from PC Specialist:

https://www.pcspecialist.co.uk/notebooks/optimusX-15/

which is £1,122 when it has the same hardware as the MSI.  (I can't send you a direct link to that configuration for whatever reason, but I can show you how to get it.)

All other options I saw are more expensive or don't have exactly what you want.

@puzzlezaddict I like the look of the Tracers and the Optimus. Do you know why laptops that work best for gaming are ones from brands that aren’t mainstream and why mainstream ones are no good for gaming?

@WallFlower26  I wouldn't say that mainstream brands are bad for gaming.  Some, like MSI, are very good.  Other companies make good high-end laptops and also cheaper options that don't always run games as well, probably because the manufacturer cut some corners to keep the price down.  But that all depends on the particular company and the specific model of laptop (or desktop).

The other issue is that many laptops are designed primarily for some other purpose, and gaming is kind of an afterthought.  A model designed to be lightweight and portable might not have the necessary cooling for games, and it probably won't have a strong enough graphics card either.  Even a laptop meant for graphic design or video editing will have hardware tailored to that, and not necessarily the best components to run games.  But gaming laptops are specifically for gaming, and as long as you get a quality one, you should be fine.

@puzzlezaddict I’ve just seen that the Tracers don’t have operating systems. On the Tracer laptop it says ‘(Note: We will install your Windows operating system on your fastest hard drive)’ do you know what that means? Do you know if the prices of the operating system and Microsoft office packages are one time costs or subscriptions on the Tracer laptop?

@WallFlower26This is the computer I use: https://www.amazon.com/dp/B07QXLFLXT/ref=psdc_13896615011_t1_B0826YDYR9 . I actually got it originally because I could do animation and 3D rendering with it. I can run The SIMS 4 on the highest settings and it runs perfectly even with all my mods and CC. I did add 1 TB memory because I have a ton of CC. The only thing I would note is if you are running the game on the highest settings might have to elevate it a little to make sure it has good airflow underneath and that PredatorSense is set to "General Gaming". I play with it on my lap for hours all the time without any problem. This computer can handle anything you do in The SIMS 4 with ease.

@WallFlower26  Cyberpower would build you the laptop of your choice, according to your instructions, then install Windows 10 on the fastest hard drive inside the laptop.  Windows is included in the price of the laptop and is a one-time purchase, just like any other time you buy a Windows 10 license.  If you want Office, you can pay extra for a yearlong subscription; the price depends on what version you want.  Scroll down to Software for a look.