Does a High Gas Fee Guarantee a Transaction Will Be Included in the Very Next Block?

No, a high gas fee does not guarantee inclusion in the very next block, but it makes it highly probable. The final decision rests with the validator chosen to propose the next block.

If the validator is using a strategy to maximize their profit, they will likely include the high-fee transaction. However, the block may be full, the validator may be malicious (censoring), or the transaction may be part of a bundle that the validator chooses to reject, preventing its inclusion.