If the rim is running true radially and laterally, and the spoke tensions are reasonable, then the wheel should be usable.
Personally I'd aim for less runout, with .3mm being about where it starts to be "close enough" and even less is better, although I'm using rim brakes on a road bike where little variances like that can make fast cornering feel decidedly disconcerting.
If you're on disk brakes with large diameter lower pressure tyres, then a 1mm runout may be undetectable to the rider
Very similar to de-stressing a wheel:
- Take out any QR or through-axle.
- Put one side of the rim on a hard concrete surface (not dirt) and put one foot on it. The hub will be resting on the concrete too -
- Then put your other foot lightly on the opposite side of the wheel - your knee will be slightly bent.
- Gently increase the pressure - there will likely be pinging noises from the hub and spokes as they relax against each other. Once the ping noises stop, rotate wheel 60 degrees and do it again to cover the whole wheel.
- Then flip the wheel over and repeat on the other side.
How much weight you apply depends on your mass. A small 50 kg person could probably put all their weight on the wheel whereas a large person would be a more restrained.
If the wheel taco's then clearly it wasn't up to the task.
Consider that a wheel has a much higher strength radially than laterally. When riding you're putting about half your mass through the wheel all the time, and there will be peak loads of double-to-triple your whole mass.
I personally have a used 26" front wheel where one spoke is literally slack - adding any tension puts the wheel out of true. And the two neighbouring spokes have relatively high tension. This wheel has worked fine for 8 years though I'm not doing jumps or stunts.
Ultimately its your decision about what is safe and what is unsafe. We can't tell you on a forum - if you remain unsure, take the wheel into a proper local bike shop that you trust for an expert's opinion. These sort of things need to be seen and felt to make a qualified suggestion.