The Auto Stand-by turns off the receiver if there is no audio or video signal for 20 minutes when set to On. Thus it shouldn't be blocking the receiver from coming on if it is set to Off. When the USB Power Out on Standby (power to a USB device when the receiver is off) or Network Standby (enable network power on requests from the Onkyo app) are enabled, then you get the hybrid standby mode if the Power Management Auto Stand-by is active (On). There is also an HDMI Standby mode for throughput of an HDMI signal.
What devices do you have connected to the receiver? Try turning on a video or audio source before you turn on the receiver. The other reasons for the unit not to turn on is the protection circuit being engaged. This can happen from overheating or a loose speaker wire touching another wire or the back of the receiver. Usually if the unit has the protection circuit engaged, the display will indicate Amp Diag Mode. After the diagnostic test, the display will indicate if there is a problem (SP wire). If there is nothing on the display after the diagnostic, the receiver should work properly when it receives an audio signal to send to the speakers. If the unit has been overheating, make sure that there is good ventilation around the receiver. Also clean any dust off the unit.
Crutchfield has the manual for the TX-RZ730 on the product page: https://www.crutchfield.com/S-lvaBRQ0O5ib/p_580RZ730/Onkyo-TX-RZ730.html
. The current link to the manual is https://pdf.crutchfieldonline.com/ImageBank/v20200223150400/Manuals/580/580RZ730.PDF
I hope this helps. If you heard an abnormal sound or smelled smoke, then the unit has internal damage. Similarly, if the problem continues, I'd suspect a wiring fault between the internal power supply and the main board of the receiver. The unit needs service or replacement.