Have a look at resource monitor whilst you run your game. There are a number of ways to run this, one is to right click the taskbar and open task manager, then on the performance tab click 'resource monitor'.
If you click on the memory tab you should see something like this:
If your memory fills up, the game will lag and possible crash as it does not have the resources to continue. As you can see I still have some free memory to work with. (Please don't laugh at my Sims computer, he was built by me a decade ago with cheap parts and he has performed admirably, I had to buy him a new CPU fan a few months ago but he is still going. If I wasn't so miserly I would have built another computer for Sims, but this one still works and he is part of the family!
)
Also, check the CPU tab:
My computer has two cores (four hyperthreads) as it's old and low powered; so if I'm running a browser and the game simultaneously, I can set the game to use a specific core(s), that way the load is more balanced. If these graphs show too much load on one or more cores, I start to get lagging as the computer cannot process the game data. I use a startup script for the game to do this.
Windows (under default conditions) uses a page file to manage memory; this is like having a notepad by your side as you are doing something- when someone tells you their phone number in a conversation, you write it down, and then later, you put that written down number back in your memory when you think about it to dial it. In the same way, Windows writes down memory information in a page file, onto the hard disk. It does this when it does not have enough memory free to use. Later, when there is some free memory, it will access that page file and read that information to memory. This is called 'paging' or 'swapping' or 'virtual memory'. But, this uses CPU power and GPU power too, as the computer needs to process the information to get it in and out of memory. So, having optimal CPU useage is important too, as well as having lots of free RAM. Otherwise things take longer, which is when you get lagging, and you also get bottlenecks (when one bit of the computer works slower than the other)- and this is when I see pink flashing, when there isn't enough RAM to get the texture information to the GPU. So the computer has nothing to show me- the game responds by giving the display some flashing pink, without the animations. The GPU is working fine, but the rest of the computer can't find the information to send to it.
So what you need to do is to find out what causes your game to struggle.
First things I would check it seems that you have already done- set the graphics rules file so that the game knows what hardware you have. Make sure your RAM and GPU are accurately identified.
Next, check your graphics chip software to see if there are any overrides. I use an NVidia chip so I have an NVidia control panel, where I can set the 3D settings for a particular game and override the game's settings (such as antialiasing). If you have pink flashing, make sure that is set to default, or game controlled. Same for any NVidia Experience settings (or the equivalent if your graphics chip has them). Let the game control everything, at least until you have it all working.
Thirdly, look at what else is running on your PC. Are you using any post processing software, reshade or anything like that? Running other applications, like a browser, or discord, or solitaire game, or iTunes? Shut them down, just until you get things sorted.
Lastly, look at your custom content. Are you using anything that can cause the game overhead to be higher? Things I can think of are- Mods that increase the resolution of in-game terrain textures, snow textures, water textures/ reflections, lot impostors, tree impostors. Remember that if you play with neighbourhood view on, everything you do in-game is impacted by the resolution of the background scenery. If you have all of this jacked up to high-res, this can eat available memory very quickly. Also, hi-poly hair can affect things, especially if you have a party or go to a community lot where 40 sims turn up with high detail hairstyles.
I don't know if any of this will help you as obviously your computer system is very different to mine, but for my low-powered, ancient thing these are the things I need to take into account. Things like Pineapple's post processing and high res snow are lovely for photos, but using whilst playing can tank performance.