Apple’s default Messages app, the one that came with your iPhone or iPad, actually uses end-to-end encryption and other pro-privacy practices. There’s also a good chance that many of your friends and family members use it, making it an excellent choice for securely sending messages without any hassle.
There are some things to note, however. If you back up your messages to iCloud, there’s a chance that a government entity could still access them. And E2E encryption only applies to the blue bubbles — those green SMS text messages aren’t encrypted at all.