If you haven't done GTA 5, that's the one you really need to get.
RDR2 is a very good game, but it's a slower pace that's not for everyone.
GTA 5 is a masterpiece for dicking around. I've spent entire evenings just stealing a waverunner and racing through the canals, or the scuba boat and scuba diving, or stealing a bike and biking up and down the mountain, or taking a helicopter up to interesting places and jumping out and parachuting.
In particular, you're going to want to check out "Director's Mode."
This is a mode where you can toggle things like turning off police reactions or giving access to guns or having a super-jump that lets you fly through the air to the roofs of buildings with one leap.
You can really enjoy some of the finer details in this mode, like shooting up cars to see the deformation physics and how the tires get flat or the specific gas tank locations for different cars where they start leaking and shooting the gas trail to blow it up.
Infinite ammo for the mini gun is also quite worth it.
Teleporting around the map is extremely convenient too for things like getting back to the top of the mountain to bike down it over and over.
And oh man — controlling the weather and time of day, and being able to freeze the time of day to exactly when you want? Keeping it at nighttime and rain for an entire play session? Hit the golden hour with an overcast sky and keep it there? Makes a huge difference too.
(The only negative of Director's Mode is you can't explore stealth mechanics and certain types of special NPCs like the mime don't show up.)
There's so much detail to the world. Get into the military base and see if you can find where one of the landing strip lights is on the fritz because the drain next to it is overflowing. Or some of the graffiti in the tunnels underneath the city.
For your specific ask, I really can't think of a better game in existence.
(I've also spent hundreds of hours messing around in Cyberpunk 2077, which is an outstanding game and open world, but not quite at the level of polish and variability as GTA 5.)
Not even that. It was placeholder textures, only the "newspaper clippings" of which was forgotten to be removed from the final game and was fixed in an update shortly after launch.
None of it was ever intended to be used in the final product and was just there as lorum ipsum equivalent shit.