To be fair, YNAB is rather explicit about how it connects to your accounts and also actively recommends against doing so in favor of manually entering your transactions. My experience with connecting the two is that I still need to manually validate every transaction because on occasion Plaid is either slow or just misses entries entirely.

Also in the case of YNAB, Plaid is not posting transactions on your accounts. It's a screen scraping service transferring account data.