For whatever reason, you may attempt to do an epic squat by yourself. Not smart, but rather than telling you to rethink your madness and skip it altogether, you can be safer with knowing how to bail when things start to look bad. This video by Omar Isuf shows you how. The usual recommendation for making heavy weightlifting attempts safer is to have a spotter whom you know, or who at least knows how to spot properly. When that's not available, the next best thing is to learn how to slip away scot-free. In Omar's video, he addresses squatting in a power rack versus a squat rack. Basically, the main difference is that a power rack has adjustable safety pins that will "catch" the barbell should you fail to lift it. If you're squatting solo, you should be squatting in a power rack and adjusting the pins to the appropriate height (about 5cm below your lowest squat position, he notes).
The other bailout technique Omar mentions is dropping the bar behind you and literally walking it out, but this technique works only if your squat form is spot on and you have a more upright position that allows you to simply roll the bar off your back. I highly recommend practising this technique with a lighter load before you attempt to roll something two or three times that off your delicate spine.
As always with heavy weightlifting, safety is numero uno. Make sure to balance out the risk (getting your back bent like a slinky) versus reward (a glorious personal best and rush of adrenaline). It's good to know how to bail out of a bad lift, so check out Omar's video for his demonstrations on how.
How to Squat Heavy Alone (100% Safely) [Omar Isuf]