So after multiple clean installs which include erasing the whole physical SSD you are having this problem? And before migrating/restoring from a backup? Have you installed any third party apps?
You can try "Restoring" the firmware which will reset the T2 security chip as well as pushing a clean OS onto the laptop's internal SSD (similar to how you restore an iPhone or iPad).
Revive or restore an Intel-based Mac using Apple Configurator - Apple Support
Make sure to disconnect all external devices in case one of them is causing a problem.
If you can boot the laptop into a full copy of macOS you can try running DriveDx to check the health of the SSD. Post the complete text report here using the "Additional Text" icon which looks like a piece of paper. While the Apple SSDs don't contain much health information, once in a while you may find something useful in the SSD's health report.
Did you perform the SMC Reset properly? The procedure has changed with the 2018+ Intel Macs. See this Apple article for details:
Reset the SMC of your Mac - Apple Support
You can also try running the Apple Diagnostics to see if any hardware issues are detected. Unfortunately the diagnostics won't detect most drive failures. Plus the only useful diagnostic is one which fails or freezes.
I suspect the SSD is failing (probably taking too long to go ready), but you could have some other issue with the Logic Board. If the above tips don't help, then you will likely need to have Apple or an Apple Authorized Service Provider examine the laptop to provide you with a repair estimate.
