Insider Build v0.15.3.
The release notes say: ‘You can now rearrange the order of tabs in the sidebar.’
This allows the sort order to be ‘custom’ set, by pressing on the ‘Drag to rearrange’ icon.
This then allows the tabs (folders and notes) to be manually sorted, by dragging-and-dropping.
However, the moment you then interact with the folders or notes, the alphabetical order is reimposed.
I don’t understand you.
There has never been an alphabetical list for sidebar panes. Drag to rearrange icon?
Post a screen recording of the problem happening in the sandbox vault.
My apologies. I am new to Obsidian. You are right–this seems to be a community plugin (Bartender, it appears), not a core function. I will delete this threat once you have seen my response, so as not to cause confusion.