According to the Wiki, the DPS for beer as a weapon is around 4.4, whereas a wooden club is 5.75. So a raider equipped with beer about 75% as strong as if they had a wooden club, which is itself a fairly weak weapon.

As for how often a raider spawns with beer, that's up to how the game distributes its raid points, which I don't know the details of nor do I try to change any of that. I'd say empirically they spawn maybe around 5% of the time among Penitent/Drifter/Thrasher raider types (i.e. the already poorly equipped types), but that'll also depend on things like difficulty too.

Just to get an idea of the impact of this mod:
1. How high is the "Comabt Power" of a pawn with a beer ?
2. Is there a rough estimate of how frequent pawn´s with beer as a weapon spawn ?

Interesting idea, but I think it would need to be a bit more complicated. I guess person who picks "beer" as weapon or any random unncomon non deadly item, should have insane trait or be high on smokeleaf/yayo or maybe spawn with brain damage. That would make it belivable.
its random wild world in edge of the galaxy, it can have some psychos.
if you make it a bit more, I will use it gladly.

I tried adding wood logs to the weapons pool too. It works, but the way the game weights weapons when equipping raiders meant that like 1 in 1000 raiders would actually generate with a log as a weapon in my testing. I might be able to get it to work better without changing the stats of wood (which could make things unbalanced in other ways) but would take more investigating.

Can you add wood logs too?