OpenBSD 7.5 bsd.upgrade hangs after sysupgrade

Hi, I tried upgrading to OpenBSD 7.5 from 7.4 using sysupgrade(8), but upon
reboot, bsd.upgrade hangs. The last messages from the boot process seem to be:

softraid0 at root
scsibus1 at softraid0: 256 targets

and then it just hangs. Keyboard is completely unresponsive, Ctrl+Alt+Delete
doesn't work, the only way I can reboot at all is cold power off by holding the
power button and subsequent power on.

The machine I am trying the upgrade is a Lenovo V15-ADA 82C7 laptop with AMD
Ryzen 3 and ATI Picasso graphics. My built-in Atheros QCA6174 WiFi card doesn't
work under OpenBSD 7.4, as I assume there is no driver written for it (yet?),
so I am using external Realtek 802.11n NIC WiFi adapter attached to a USB port.

The first attached image is when I tried booting after sysupgrade with `boot
-c`, then disabling radeondrm (as suggested in some Google search results) and
turning on the `verbose` option.

The second attached image is from trying to boot from install75.img written to
a USB flash medium.

As can be seen, both options hang in the same way.

I'd appreciate some pointers on how to debug or solve this.

Thanks in advance,
Strahinya