Try this,
Under controls section, in the fallout_Default.ini, change the following lines to 0:
fForegroundMouseAccelBase=0
fForegroundMouseAccelTop=0
fForegroundMouseBase=0
fForegroundMouseMult=0
If these don't work, give me a shoutout so we may try something different.
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Fiber To The Home (FTTH) network engineer (post-gratuate)
Cardio pneumology physiologist (ESSEM university)