So, if you haven't heard yet, Linux Mint 19.1 has had a BETA released for it which includes Cinnamon 4.0, and all the other latest additions and such for it, and here's how things are right now with getting Feren OS ready for Cinnamon 4.0:
If you haven't been checking the Feren OS Twitter recently, every single themer theme has been updated to bring with them changes to make them better support Cinnamon 4.0, since PanelSizeup='s changed values no longer exist in Cinnamon 4.0's settings, including the Yosembiance theme too (even though that's basically dead by now for 18.04+ users). The main changes are that Themer Store now has the latest themes available for every theme, not just the non-Feren-OS-included themes, every theme no longer changes the PanelSizeup value, every theme has lost install-commands, sysfols, and apply-theme (excluding macOS Themes which use apply-theme for Docky changes), every theme no longer has MessagingMenu as an applet, and every theme now uses Grouped Window List.
Themer itself also got updates, ditching sysfols and install-commands support, adding code to make themes install one at a time instead of running while another is running, automatically replacing Grouped Window List with IcingTaskManager for non-Cinnamon-4.0-users, and adding a warning screen for themes setting 'PanelSizeup' still. Also, the dialog for a successful theme install should now be able to name the theme every time normally, as long as the theme has not got illegal symbols on its name.
Finally, on the subject of themes with noticeable updates:
Linux Mint Layout - This theme now uses the Modern Layout, the layout introduced to Linux Mint by default in 19.1, using the 19.1 BETA panel layout, size, etc.
Linux Mint - Same change as the layout version, but it also now lets you pick a Mint-Y colour scheme following the choice of Light, Dark or Darker (this second dialogue won't appear until the 19.1 update is released, as the theme settings program for the Mint Theme checks to make sure there's colour variants available before offering them to the user).
Adapta - There's now a configurator for this theme, letting you switch between Light, Light Compact (Eta), Dark and Dark Compact (Nokto Eta).
macOS, Mac OS X, etc. - Docky should launch automatically once more upon the theme being changed to one of these
For Cinnamon 4.0, the Cinnamon configurations will see updates adding default values for some new settings in 4.0 and removing depreciated/removed settings values from the default settings, however this will come later, and these updates will be dependency-locked to Cinnamon 4.0+ due to the removal of values lost in 4.0...
Applet Updates, Theme Updates, etc:
Obviously, given it's Cinnamon 4.0, to retain stability with 4.0's changes the applets will see updates released for them system-wide.
As well as this, the themes will be updated to add theming to the Grouped Window List applet, since it has new theme values that aren't changed by the default Feren OS themes currently.
Given Mint 19.1 hasn't really got anything much new in the form of other packages that can be completely deemed necessary for installation on their own, the update procedure will hopefully just be that updates are released, then the Feren OS Repository/PPA Settings package gets updated to bring the repos to LM 19.1 from LM 19.0, and lastly the Major Updater gets a script update to have it upgrade to Tessa instead of Tara for the Mint Repositories part of the procedure.
The Feren OS Dev
It's great making something for the community that might become quite big and remain for a very long time to continue serving the community and helping Linux as a result.