Uncle blocks were produced before the merge when two miners found a solution at the same time and following blocks were appended to only one of them. So my question is, are uncle/ommer blocks still possible after the merge?
In the post-merge PoS Ethereum, validators will be pre-selected to validate blocks, which means that no more than one validator will be validating a block at a time. Hence, there are no uncle (ommer) blocks created. Also, the ommer field in the block header (from PoW Ethereum) will be empty as it's unused and irrelevant in post-merge PoS Ethereum.