So there is "spam" in your knots mempool, you just don't tell others about it?
Or is it cached somewhere else?
Some mempool policies in core will always restrict transactions for various reasons. They still exist in core.
In an ideal world all nodes will have the same mempool but it's not the case in reality.
Rejected transactions are saved but not relayed and there are options to set the size in knots: https://github.com/bitcoinknots/bitcoin/blob/v29.1.knots20250903/doc/release-notes.md#p2p-and-network-changes
