Literally dozens. Like 24? 36? I didn't know there were dozens of sandbox simulation racing games. I have the 6 that I use but let me know what the other 30 are. Always looking for more.
I know you're trying to be a smart arse, but let me open Steam.
Assetto Corsa
ACC
Automobilista
Automobilista 2
BeamNG
Copa Petrobras de Marcas
Dirt Rally
Dirt Rally 2
FM7
GP Legends
GT Legends
GTR
GTR2
Live for Speed
netKar Pro
pCARS
pCARS 2
R3E
Race 07
RBR
rFactor
rFactor 2
That's 22. (Note: not all of those are sold through Steam, I just link external games through Steam as a launcher for convenience.)
Then there's stuff I actually own on console with the hardware to play it:
Gran Turismo 3
Gran Turismo 4
Gran Turismo 5
Gran Turismo 6
FM 2
FM 3
FM 4
There's another 7, so we're up to 29 already. I do have GT 1 and 2, but they're neither much of a simulation nor much of a sandbox by modern standards. And yes, I gave up on buying consoles after the PS3/360 era, or there would be GTS/GT7 and FM5/FM6 in there.
Then there's a bunch of stuff that is either not as sandboxy or not as simulation-y.
Codies F1 games. I think I have about six of them over the last decade and a bit over several platforms.
WRC7
Ferrari Challenge Trofeo Pirelli
iRacing (sub lapsed at the moment, but my account has a fair bit of content)
Forza Horizon 1, 3, 4 and 5 - simulation is marginal but as a sandbox they're fantastic.
So that's another 13 maybes, so realistically what I have is somewhere between 28 and 41 depending on what you want to consider as qualifying. A lot of these are still worth playing if you haven't, they almost all have at least one unique feature that makes them interesting. The older ones will be harder to get into unless you're interested in sim racing history - they can take a bit of work to get running well on modern hardware and control systems, but it can be fun seeing just how good some of the old sims really were.
In terms of ones I actually play more than once a year though, there's not that many. AC/ACC, AMS2, BeamNG, DR2, F12020, pC2, FM7, FH5. The only thing that those games don't cover well is online racing, but I just don't have time for that these days so I don't care.
And a career mode, obviously, but very few games do that well which was the whole point of my original post.