system freeze older iMac Debian 11

["Robert F. Crochelt" <rfc56@fastmail.com>]

Hi
Older iMac, recently installed Debian 11.  Having system freezes even
when running light weight environment like fvwm.  Starts with slow
video, progresses over a few minutes to complete freeze.  Can't even
shift to a different console with ctrl-F_.  Nothing in top (when it
starts) to suggest excessive memory or cpu usage.  Tried to install
nvidia drivers, but apparently not available for my GPU in Debian 11.
Output from lscpu and nvdia-detect in attached file.
I would be grateful for any suggestions.
Thanks
Bob Crochelt

Detected NVIDIA GPUs:
01:00.0 VGA compatible controller [0300]: NVIDIA Corporation G92M [GeForce 8800M GTS] [10de:0609] (rev a2)

Checking card:  NVIDIA Corporation G92M [GeForce 8800M GTS] (rev a2)
Your card is only supported by the 340 legacy drivers series, which is only available up to buster.


Architecture:                    x86_64
CPU op-mode(s):                  32-bit, 64-bit
Byte Order:                      Little Endian
Address sizes:                   36 bits physical, 48 bits virtual
CPU(s):                          2
On-line CPU(s) list:             0,1
Thread(s) per core:              1
Core(s) per socket:              2
Socket(s):                       1
NUMA node(s):                    1
Vendor ID:                       GenuineIntel
CPU family:                      6
Model:                           23
Model name:                      Intel(R) Core(TM)2 Duo CPU     E8435  @ 3.06GHz
Stepping:                        6
CPU MHz:                         797.956
CPU max MHz:                     3066.0000
CPU min MHz:                     800.0000
BogoMIPS:                        6117.66
Virtualization:                  VT-x
L1d cache:                       64 KiB
L1i cache:                       64 KiB
L2 cache:                        6 MiB
NUMA node0 CPU(s):               0,1
Vulnerability Itlb multihit:     KVM: Mitigation: VMX disabled
Vulnerability L1tf:              Mitigation; PTE Inversion; VMX EPT disabled
Vulnerability Mds:               Vulnerable: Clear CPU buffers attempted, no microcode; SMT disabled
Vulnerability Meltdown:          Mitigation; PTI
Vulnerability Spec store bypass: Vulnerable
Vulnerability Spectre v1:        Mitigation; usercopy/swapgs barriers and __user pointer sanitization
Vulnerability Spectre v2:        Mitigation; Full generic retpoline, STIBP disabled, RSB filling
Vulnerability Srbds:             Not affected
Vulnerability Tsx async abort:   Not affected
Flags:                           fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good nopl cpuid aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm sse4_1 lahf_lm pti tpr_shadow vnmi flexpriority vpid dtherm