Necroing, because the solution hasn't been documented here.
I have GTX 1070 as well, and I could get to the point of loading the world, but if I try to link any other maps (i.e., shopping, nightlife, whatever) it crashes. Initially, the client wouldn't even launch, but I started playing around with settings and was able to get through world selection, but doing anything beyond that point would crash the client. After looking at the exception files the client was generating, I was able to isolate the issue.
Dug through dozens of troubleshooting threads, but only found one that worked.
Troubleshooting steps I took with little/no success
1. Started by setting the game to run in windowed mode. In the Origin UI, right click on TS2, select game properties, click on advanced launch options, type -w in command line arguments. Made launching faster.
2. As per this thread, I changed the compatibility settings and ran as administrator, which made the game crash before launching - basically making the issue worse.
3. I dug into the exception files and saw I was getting the ACCESS_VIOLATION error (you can check this in Documents\EA Games\The Sims™ 2 Ultimate Collection\Logs in text file named Sims2Exception with the date and time of the exception). According to the amazing celebkiriedhel of Leefish, "An Access Violation occurs when the game tries to write something where it shouldn't. Rather than overwriting a piece of code it gives the violation and stops." Part of that seems to be because the game was last updated before a lot of modern cards were released, and it can't recognize the cards without changing the graphics card texture fix to graphics rules.sgr and updating the video card on the video cards.sgr.
What ACTUALLY worked for me:
I decided to run Graphic Rules Maker (GRM) by Sims Network, which was updated for 2020, as it autodetects the installed graphics card and modifies settings automatically without needing to manually adjust the .sgr files (which is what I had to do with TS3 to get it to run..). Kiri mentions that sometimes GRM misses certain details, so I decided to apply GRM, then double-check the files with the Leefish guide to ensure everything was updated properly (thread titled "Sims 2 - UC Access_Violation Error after Windows 10 updated").
If that gets censored out, the issue is that the game is old and doesn't recognize new cards, and that's why powerful systems are crashing when running what should be a super low-resource game. Superficially low memory limitations can create an endless loop that winds up eating all of your memory, and crashing the game. You have to repair the graphics rules.sgr and video cards.sgr in order for the game to recognize your cards - there is a program that does it automatically, which should be easy to track down just by searching "Sims Network Graphics Rules Maker" or "Sims 2 Ultimate windows 10 not recognizing graphics card." The program is a direct executable file, and did not cause any issues or flag my malware - it's reputable within the community. If you'd still prefer not to run it, Leefish has a guide to manually update the files, but it can be quite confusing if you're not used to modifying files that are severely outdated.
As always, backup your game before making any modifications to the game files.
EA isn't going to provide an update on this, and as the title is so old, these steps will be necessary to run the client without crashing on newer machines.