Our upcoming releases (Sigil-2.0 and PageEdit-2.0) will use Qt6.5.2. Plugins that use a Qt gui will move from PyQt5 to PySide6.

As a result, the new minimum supported version for macOS will be macOS 11.0 (Big Sur) as earlier macOS versions are no longer getting security updates from Apple. If you are using a mac with an earlier version of macOS we strongly encourage you to update to at least Big Sur if possible and up to Ventura if you can to keep getting critical fixes from Apple.

The new minimum supported version for Windows will be Windows 10 (build 1809). In addition, there will no longer be an official 32-bit Windows binary installer provided with Sigil releases starting with 2.0. 64-bit only. I (Diapson/Doug) will attempt to maintain an unofficial 32-bit legacy installer in my personal Github repositories, but I don’t know how long I will be able keep that up. It may not be updated every time a new version of the official Sigil is released.

Linux distros (and those who compile Sigil and PageEdit themselves) will still be free to choose if Qt5 or Qt6 makes more sense for them.

The reasons for this move are many and were driven primarily by security concerns and the lack of newer platform support in the older Qt versions.

The released source code for Qt5.15.9 and Qt5.15.10 are now missing quite a number of CVE (critical security) fixes and QtWebEngine/Chrome security fixes. They are also missing full support for newer platforms such as arm64 based Macs.

All of this was caused by a change in Qt’s policy to delay each of the Qt5.15.x source code releases (afterQt 5.15.3) by 12 months or more leading to critical and security fixes not being applied or even sometimes collected.

There are now literally numerous third party efforts to try to keep Qt5.15.x source code more secure and up to date but each are missing bug fixes important to one platform or another and us chasing those down would quickly bring Sigil snd PageEdit development to its knees.

In addition we simply do not want the potential mental liability of releasing a version of Sigil with known missing or spotty security updates and without critical bug fixed on the very first day of a Sigil release.

Therefore we need to move Sigil and PageEdit closer to the development forefront of the Qt (Qt6.5.2 released last week) to make sure what we release is the most secure it can be on its release day.

We understand that this change may leave users of older Linux, Mac, and Windows machines behind. So we plan to keep the Sigil and PageEdit source code buildable using Qt5 on older platforms for at least the next year, but leave producing those release binaries up to interested parties.

For most users, each new Sigil/PageEdit release will continue to perform just as it has before, but will be more secure with more bugs fixed. In addition, almost all Sigil plugins will continue to work just as before.

For those plugins that used PyQt5 as a gui previously, we have provided plugin developers with a utility module to use that allows either PyQt5 or PySide6 to work. And of course plugins that use tk or have no gui are not impacted by the move at all. Many of the Qt plugins in our Plugins thread here at Mobileread have already been updated to accommodate this change. And we are, of course, happy to help any plugin devs that use a Qt gui update their plugins for PySide6.

In addition, there’s a wealth of information about modifying Qt plugins to work with the older and newer Sigil versions in the following thread: https://www.mobileread.com/forums/showthread.php?t=346162. Including plugin templates and examples that show how to use the utilities module to maintain compatibility with all versions of Sigil.

Thank you.

Your Sigil Development Team.

See also this previous post for more relevant info.