Another alternative is to have Origin logged in on another computer and then launch it you'll be notified that you're logged in elsewhere and asked if you want to continue in off-line mode (my daughter and I experience this all the time). You can then re-enable the internet and Origin will remain offline. It will notify you that you are offline and ask for you to log in (even though you aren't online). You can temporarily disable your internet (easy on a laptop, not so sure about a desktop) and launch Origin. MrsFlynn's instructions are perfect for going offline, but there's a way to launch Origin in off-line mode to start if that's your preference. If you purchased/installed through Origin, I have no idea if you can by-pass it. I use TS3.exe to by-passes the launcher, or I use Sims3Launcher.exe to see the launcher first. I don't use the expansion directory my files are in: \\\Program Files (x86)\Electronic Arts\The Sims 3\Game\Bin\. For a long while, a subsection of simmers has been desperate to see multiplayer capabilities return to The Sims franchise, from those who miss the full-on. FIFA 22 Madden NFL 22 Battlefield 2042 Apex Legends The Sims 4 It Takes Two Electronic Arts.
However, I purchased and installed them prior to Origin (but I am able to play through Origin if I want). Another Sims 4 Mod Promises Multiplayer - But Does It Work Another The Sims 4 mod has launched, allowing simmers to play with their friends within the same household. Origin Access costs either 5 per month, or 30 per year.
I have two files that I use to play TS3 without Origin.