I believe this is intentional. If in Blender 2.93 you modified the default theme rather than create a new theme, then you import your settings to Blender 3.0, the theme will be reset to the default of 3.0. This is done to ensure that everyone who's using the default theme in Blender gets the new default theme in Blender 3.0. However it means that if you modified the default theme, it will not be carried over to the new Blender.

To "fix" this on your end, please save your theme as a new theme. This can be done by:

1. Open Blender 2.93.
2. Select from the top of Blender Edit -> Preferences
3. Go to the Themes section of the preferences window.
4. At the top of the Themes section you will find a part labeled Presets. Press the Plus (+) icon beside that Presets section.
5. Give your theme a name, press Ok then save your preferences if you have disabled auto-saving.
6. Open Blender 3.0, import your 2.93 settings, and then you might have to go back to the Themes section of preferences and select your theme from the drop down.

In T93088#1253756, @Alaska (Alaska) wrote:

I believe this is intentional. If in Blender 2.93 you modified the default theme rather than create a new theme, then you import your settings to Blender 3.0, the theme will be reset to the default of 3.0. This is done to ensure that everyone who's using the default theme in Blender gets the new default theme in Blender 3.0. However it means that if you modified the default theme, it will not be carried over to the new Blender.

To "fix" this on your end, please save your theme as a new theme. This can be done by:

1. Open Blender 2.93.
2. Select from the top of Blender Edit -> Preferences
3. Go to the Themes section of the preferences window.
4. At the top of the Themes section you will find a part labeled Presets. Press the Plus (+) icon beside that Presets section.
5. Give your theme a name, press Ok then save your preferences if you have disabled auto-saving.
6. Open Blender 3.0, import your 2.93 settings, and then you might have to go back to the Themes section of preferences and select your theme from the drop down.

This is incorrect. I have not modified the default theme. I have modified my own theme. When you modify any theme, the modification of the theme results into the selected theme option falling back to "Presets" state. But the "Presets" state does not guarantee the last modified theme was the default one.

This is probably the due to the embarrassing fact that Blender still does not have any option to save the theme modification. Only option to save the theme modification is to use the UI element to create a new theme, and name the new theme exactly the same as the one you intend to modify, creating significant room for error. Until this issue is resolved, more issues like this one are likely to arise in the future.

If the last step of the process is "Open Blender 3.0, import your 2.93 settings, and then you might have to go back to the Themes section of preferences and select your theme from the drop down.", then the "Load 2.93 settings" feature is clearly broken or does not work as expected. It's no different than for example keymap not loading properly, and the solution being telling user to go to settings and select his keymap. This feature is expected to load all the settings for users, with no exceptions, so that there is absolutely no uncertainty whether some settings were left unmigrated.

If the goal is to make sure that the users receive new, updated 3.0 default theme, then the check should be whether the state of theme selection in 2.93 was set to one of the default themes (Blender Dark or Blender Light), and in such case, skip migration of these two theme files from 2.93. If the state of the theme selection is fallen back to "Presets", then it can not be guaranteed that the user has used default, unmodified Blender theme.