1 sat/vbyte is a relay rule, not a consensus rule: a 0 fee tx is perfectly valid. Nodes don't relay tx with less than 1 sat/vbyte to prevent spam attacks, but they accept 0 fee txs in blocks.

This limitation was introduced when BTC was worth a couple of bucks, it can be lowered to 0.1 sats/vbyte (or even lower) while maintaining the original security assumptions.

So, a 138 vbytes tx would need to pay at least 14 sats to be relayed by the nodes.