I did it like this:

• You need to have custom theme you can follow this
• For the RichEditor i added a class to make its size fixed.You can choose the size you like

RichEditor::make('editor') ->extraInputAttributes(['class' => 'max-h-96'])

• In your custom theme css file mainly found on resources/css/filament/admin/theme.css you should add the following to make the toolbar sticky:

  trix-toolbar { @apply !sticky top-0 z-[19] bg-white; }