IRF540Z-class D power

There is a layout-dependent amount of overshoot on Vds that limits the maximum practical supply voltage for reliable operation. Supply pumping may be also a concern.

If you take a close look at the Vds of the low side MOSFET while switching high currents, you may see the overshoot.

Cross-conduction, if any, is another limiting factor. The more precise the switching "sequencing", the more close you can get to the limits.