Try: Disable text selection for post content placeholder block.

Author: jasmussen

packages/block-library/src/editor.scss

@@ -54,6 +54,7 @@
 @import "./query-pagination-numbers/editor.scss";
 @import "./post-featured-image/editor.scss";
 @import "./post-comments-form/editor.scss";
+@import "./post-content/editor.scss";
 
 @import "./editor-elements.scss";
 

packages/block-library/src/post-content/editor.scss

@@ -0,0 +1,4 @@
+// Disable text selection in the post content placeholder.
+.wp-block-post-content.wp-block-post-content {
+	user-select: none;
+}