I do have silver enabled to spawn in the nether, but not in the overworld...

list of mods:

proof:

Working to replicate this. Are you able to provide the seed and coordinates for where you found this?

I just had the same thing happen myself today. Forge version 1.16.5-5.5.0.
Modlist:

Seed: 7683363644388113742

I know what causes this. Do you have large ore deposits installed? That mod causes large veins of ores to rarely appear in the overworld, but the ores it chooses can include ores meant to be from other dimensions.