Bug#977043: fwupdmgr trap invalid opcode ip:4247d0 sp:bf98504c error:0 in fwupdmgr[423000+15000]
without being involved in packaging fwupd I tried to
have a look at this issue.
I could not reproduce it inside a i386 qemu VM (not even
with "-cpu pentium"). Have not tested on real hardware.
Looking up the endbr32 instruction, it seems it belongs to something
called "Control-flow Enforcement Technology" (CET, indirect branch) .
The opcode for this instruction got selected to run on old
CPUs as NOP, but it looks like your CPU handles it differently.
From the system name it is some "geode" CPU?
(In  someone mentions also a illegal instruction
for a geode CPU with the endbr32 instruction.)
Maybe you could add to this bug report the output of
'lscpu' or 'cat /proc/cpuinfo' ?
Then the maintainer might be able to tell if this CPU
meets the Debian baseline requirements for bullseye.
(, maybe outdated? Is there a better "baseline" description?)