The one I have in place now is an upside down T, with the vertical part fitting in the groove of the cover and the "top" resting on the engine. It works great but since it came with the truck many years ago I don't know if it's Toyota. I have had it on and off a few times over the years and it has held up well.
However, I ordered a new Toyota gasket recently just to have, and it is neither a T or an L, just an "I" kind of thing, thin enough to push partly up into the groove and have a small amount exposed out to make contact with the top of the engine. Haven't tried it yet.
The new Toyota valve cover gasket is black rubber. Like O ring rubber.
Tip when replacing it:
Remove the old one and clean out the groove in the cover. Degrease the groove too. Put a small dab of black RTV at the corners and maybe mid way. Install the gasket and set it gasket down on a flat smooth surface with a weight on top until you think the rtv has cured enough.
Then install the cover.
Without a little adhesive on the gasket, it's really easy for the new gasket to fall out of the groove when fiddling with the cover trying to get it on the head. It usually happens in the rear where you can't see it, then when you clamp down the bolts, the cover pinches the out of place gasket (ruining it) and you find out later will oil dribbling down the engine.