Senden's infrastructure is operated by wireway.ch, who has been running privacy respecting services for years before Senden existed.
Past and current projects hosted by the same operator include Streamshare, Transmit.icu, Piped, Repiped, and several smaller services. Together, those projects have served more than 2.2 million users over the past two years, without a single privacy compromise, data leak, or breach of user trust.
That's obviously not a guarantee that nothing will ever go wrong, but it shows that we are capable of running and sustaining such services. Senden is built on the same principles and run by the same people who have already been trusted by many other users.