3.1 is about two things: not losing your place when you switch devices, and not getting spoiled while you catch up.
iCloud Sync runs on its own
Turn iCloud Sync on and it just runs now, on iPhone and iPad. Your reading position and your library sync in the background, and there's a new Devices card that shows what each device was reading.
It's separate from your Boundless account. iCloud Sync goes to your own iCloud.
Handoff
Handoff is in. Start a chapter on one device and carry on with it on another iPhone, iPad or Mac that's signed into the same Apple ID.
Handoff and iCloud Sync are Apple only, and Mac gets Handoff but not iCloud Sync.
Spoiler blur in comments
Comments from chapters you haven't read are blurred, so the comments can't ruin the chapter before you get to it. A filter sets how much you see: this chapter, up to your chapter, or everything.
MangaBaka volumes and Discover
MangaBaka gets more of the app. Upcoming Releases shows confirmed volume release dates, series pages have a Volumes strip, and there are links through to publishers.
Browse has MangaBaka Discover now. Rising and Hidden gems are there for everyone, and you get personalized picks once you connect MangaBaka.
Publisher names on series info broke when MangaBaka changed its API. They're right again.
Mac updates itself
From 3.1.0, Boundless on Mac checks for updates by itself, so you stop having to go and look. The DMG is notarized, and it comes as a universal build plus separate Apple Silicon and Intel ones.
3.1.1
Three small fixes.
Settings was showing the wrong version number. The Android update check had the same problem: on installs from GitHub it kept saying 3.1.0 was available, over and over. It reads the real version now, so GitHub installs on 3.1.0 will see this update.
On foldables like the Galaxy Z Fold, Quick Settings and the other reader sheets were cut off at a half open fold. They fit now.
Checksums for every file are on the 3.1.0 and 3.1.1 release pages.