The F35's stealth is fine, that's not the problem.
The first problem is that it doesn't work very often. It require extensive, constant maintenance with even more of the usual specialized tools and infrastructure than your average modern airplane, which is a lot.
That's where we get to the second problem, it theoretically can work away from a dedicated airfield, but that brings its sortie rate, which is already bad, down in the gutter.
Which brings us back to the problem of it's fine when it works but it doesn't work.
And so this brings us to the actual main problem with the F35. It requires well maintained, expensive airfields. The Russians have missiles out the ass to hit airfields with. NATO air defense is garbage, making it impossible for us to defend said airfields from said missiles.
In the event of a war of some kind against Russia, the F35 will not be shot down, first because most of them will be destroyed on the ground and second because the remaining ones will barely every get to take flight.
What will happen is that you will see a series of successful airstrikes blown way out of proportion by the usual propaganda outlets. This will go on for like a week or two, followed by a collapse of sortie rates.
The Russians drop hundreds of precision munitions of Ukraine every week. NATO can't keep that pace up and by the end of the first month you'll see dozens of strikes on Russian targets and hundreds of strikes on NATO targets.
That's the actual problem with the F35. Along with of course the massive costs which could have been spent on missiles or drones or whatever have you. People point out that the F35 program eventually produced results, but that decade of delay and billions of dollars wasted on getting it all fixed and functional are still irrevocably gone.