The new icons are awful, but there’s a way to change them back with a free Chrome extension. The extension has some bugs, but you might be willing to deal with them to fix the icon design.

Chrome's new Task Manager brings dedicated tabs for system processes, extensions, & tabs, along a search bar to find specific ...

However, this doesn’t disable the feature altogether; you can still create new Tab groups ... across devices. Chrome allows you to save tab groups, which appear as icons in the bookmarks bar.