There is an issue where iCloud sync no longer works on older operating systems and fails with the following error message:

Failed to synchronize iCloud data. Operation is no longer supported for this container.

Apple’s iCloud service deprecated an operation and their servers started to return an error. For older iOS/macOS system versions, requests are rejected by iCloud servers, which is a non-recoverable error. On newer operating systems, it’s just a “bad request” that gets ignored by the app.

Yomu v3.7.0 should fix this iCloud bug. Otherwise you would need to upgrade your iPhone/iPad/Mac operating system to the latest version, which should solve the problem as well.

Yomu uses Apple’s default text selection, which can sometimes be unreliable. For example, the behaviour (and issues) are similar to when text is selected in the standard Safari browser.

What usually works best is to:

1. Long press on an individual word
2. Adjust the selection handles afterwards

It has already been improved in recent OS versions, it’s recommended to update your device to the latest system version. There will likely be more optimizations in upcoming platform updates. Please report issues related to text selection directly to Apple:
https://www.apple.com/feedback/

Text selection no longer works as expected with macOS 15+ (Sequoia). While it’s still possible to select text, the current selection can not be changed anymore. For example, if there is a selection like “some words in a sentence”, it can’t be shortened to just “some words”.

It’s a system level issue that affects all Mac Catalyst apps. Apple has identified a potential fix, it should be resolved in the macOS 15.4 update.

Text selection and highlights depend on the content and structure of a book. It should work in most cases, but sometimes it fails.

Content without structured or semantic markup can’t always be rendered correctly and creating annotations can fail. This is often a problem with old formats or converted books that lack any structured content.

Highlights also change the structure of a document. For example, multiple highlights in the same paragraph or with italics and links can’t always be displayed correctly. Text should still be extracted, but the highlight can’t be created anymore.

Search as well changes the structure, highlights that contain search terms can fail. The original text selection is saved and should be highlighted when you reopen a book. It’s recommended to clear search results before creating annotations.

How text is displayed depends on the encoding of a book. Unfortunately, encoding for certain special characters is not always handled correctly for some older ebook formats. This can result in for example quotes, apostrophes or other characters being garbled.

It appears to be an issue in one of Apple’s components. A recent version of Yomu added a workaround that should solve the problem. But there might still be cases where it doesn’t work or otherwise causes troubles. Please send the corresponding files to support for further investigation.

As an alternative, you can also convert such books using Calibre and reimport them, which should fix the problem as well.

1. Install calibre ebook manager
2. Add and select books to convert
3. Configure EPUB output options
   • Output format: EPUB
   • EPUB version: 2

Or you could also use the Modify ePub calibre plugin with the Encode HTML in UTF-8 option to clean up invalid encoding.

On macOS, you can right click text to get a context menu to create highlights or notes. Context menus don’t work as expected on Monterey, but this macOS issue should be fixed with Ventura. It’s recommended to use the toolbar or keyboard shortcuts for highlights, notes or other text selection actions.

Please note that “Define” and “Translate” are not available on Mac because Apple doesn’t support the required frameworks for these features on that platform.

Saving images uses Apple’s Photos framework like on iOS. It only asks for the permission once, but you should be able to change it later in the settings.

But somehow the Photos permission is not available in the Mac settings anymore and can no longer be updated. Most likely this is an issue with either Apple’s framework or system settings.

As a workaround, you can reset all permissions for Yomu on Mac with the following Terminal command. You will be ask for it again the next time you save an image:
tccutil reset All net.cecinestpasparis.yomu

Due to a bug in macOS 11.4+, layout rendering for some Mac Catalyst apps no longer works as expected when an external monitor is connected. While the correct content is initially displayed, it breaks the more you scroll or change a page.

According to Apple, a system-level fix is required. It should now work again with macOS 12, but unfortunately a patch for macOS 11 will not be released. There is no workaround available and you will need to either update to macOS 12 or disconnect external displays.