https://www.planetminecraft.com/data-pack/visiblemarkers/
VisibleMarkers is a Minecraft datapack for mapmaker's that works with marker entities. In 1.17 Mojang added these to give all datapack and commandblock freaks an easy and lag-free way to mark positions with entities. However, these are not shown to the client and this can make debugging their techniques harder. For this I created this datapack which gives you the possibility to display markers.
To use the datapack, simply drag this folder into the datapacks folder inside your world folder.
Once you have done this, you must either restart the world or type /reload in the chat.
If you now enter the command /function visiblemarkers:enable in the chat line, the datapack is ready to use.
If you have followed the instructions above, you can now use the command /trigger showmarker and the markers will be displayed.
To disable this, simply repeat the command and marker entities will no longer be displayed.
Very simple! You have to give all players who are allowed to use the command the tag showmarker. This can be done with the following command: /tag Ceddix add showmarker.
Afterwards you have to restart the world again, use /reload or enter /function visiblemarkers:enable and all players with the tag can display the marker entities.