To reproduce
Create an installation with an old version X
Launch that version
→ You get the player safety warningCheck the check mark so that you no longer get the warning for that installation
Close Minecraft
Change the version of that installation to another old version Y
Launch that version
→ ❌ You get the player safety warning again
("old version" = before 1.16.4)
Comments 2
We designed it this way on purpose. The warning screen is shown in a combination of installation and version - if any of the two is changed we will give the player another chance to decide if they want to hide the message every time.
That means that if you change the version of your installation, or duplicate an existing installation, it will be shown.
Can confirm 🙂