Java Windowsbuilder is not showing anything in the design tab and no class name in the main tab
Go to Help -> Eclipse Marketplace -> filter by popular and click install on WindowBuilder. I had a similar error some time ago because I've installed WindowBuiler by installing the separate dependencies instead of click the install button in the marketplace
WindowBuilder 1.9.5 not showing design tab after re import project
According to the screenshot, you opened the MainFraime.java file with the regular Java editor instead of the WindowBuilder editor.
Right-click the file and choose Open With > WindowBuilder Editor (see WindowBuilder Pro User Guide - Editing Existing Windows).
Please note, since Eclipse 2020-12 (4.18) Open With > ... no longer remembers the chosen editor to open that file next time. This means double-clicking a file always opens the file with the default editor which is for *.java files the regular Java editor, not the WindowBuilder editor.
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