I like the behind the trigger crossbolt safeties common on semi autos & pump shotguns.
Were any over under shotguns ever made with crossbolt safeties?

Barrel selectors, probably. Had an Ithaca/SKB SBS with the selector there. Never saw a safety there, but there’ve been a bunch of O/Us made. Who knows what those tricky Germans have wrought?

Can't recall ever seeing a cross-bolt trigger-guard safety on any double-barreled shotgun, whether O/U or SxS, And kinda doubt any German manufacturer did it!

I think it would be dangerous to say there's never been one, but I can't recall ever seeing one. I've seen and shot the odd single with a crossbolt behind the trigger, but never a double. There again, there have been all sorts of safety designs over the years - I've even seen double guns with grip safeties. However it strikes me that there are good reasons most doubles (SxS and O/U) have a tang safety. I've shot guns with cross-bolt safeties both in front of the trigger and behind, with a safety in front of the trigger which pushes forward, Greener side safeties and probably some others, and I far prefer a non-automatic tang safety for speed and convenience. YMMV

Like Mule Deer said can't recall one, most are on the barrel selector

I doubt it too, but have learned to never say never about most things. Actually, that SKB selector was in the rear of the trigger itself, not the guard. Pretty little gun, but I struggled to hit anything with it.

My new CZ has a non-automatic safety with the selector on it and mechanical triggers. Only complaint is that you can’t switch barrels with the safety off. Don’t know if that’s typical for the type as it’s my first.

I haven't seen any

The best safety I saw was on Remington 3200.

My older Weatherby Orion (SKB manufacture) has the barrel selector on the trigger. It certainly looks like a safety, but alas it is not.

My Manufrance Ideal has the safety alongside the trigger and slides forward and back. My BRNO has the safety in the front of the trigger guard and slides forward and back. My two hammerless drillings have Greener side safeties. And finally my Darne has a little lever on the left side of the receiver that rotates.

Yeah, those barrel selector sure do multi-task.