In the new SF version the tile image is removed as described in the release notes: Releases 2022.1 | Field Tile image removed
Part of this change is also the possibility on the theme level to disable the display of icons on "Document tab" or "Container tab". When disabling icons at the container level (Themes > General > Tabs > Icon), icons which are assigned as screen components tab icons remain visible.
It seems obvious to me that your choice of theme should override this, agree?
Unfortunately, this idea has not received any votes. Because we want to keep the focus on ideas that are in high demand in our Thinkwise Community, we are closing this idea.