See here for a solution that works with Sublime Text 3: https://stackoverflow.com/questions/60056867/sublime-text-3-renaming-file-tabs/60057681#60057681
Got many tabs that aren't saved files and have either 'untitled' or other useless stuff as a title?
Install this package via Package Control or manually and rename those tabs!
Press Alt+W to open the rename-panel for the currently active tab, or select Rename Tab from the tab's context menu.