If an annotation is use in a project, AutoCAD Plant 3D doesn't allow removing it. Hence, if PlantSync shows that an annotation which is supposed to be deleted since it's not longer in use in the source project, it is not possible to remove it in the target project.

To solve this you need to make sure the the annotation which is supposed to be deleted in the target project, is no longer used in the target project. So you may change the AnnotationStyleName in the target project. The next time you run PlantSync the annotation can be deleted.
 

In the source project the AnnotationStyleName is set to an annotation which doesn't exist in the target project.

You may want to consider selecting Add Annotations too so the missing annotation will be added to the target project too.
 

In AutoCAD Plant 3D a value for properties can either be set directly for the class you currently work on or the value can be inherited from the base class meaning from the class above the class you are working on. Unfortunately you can see which way it is set, because AutoCAD Plant 3D just shows the value.

Since there are two ways we synchronize the property/attribute the in the same way as it is set in the source project. So for you this is very likely just an information.
 

Here again it has to do with the way a property/attribute gets its data.

Again just an information.
 

AutoCAD Plant 3D doesn't allow deleting (actually in the Project Setup you use right-click and Purge) a class. So of course PlantSync doesn't allow removing a class in the target project even though it's not used in the source project.
 

This means that there is a property with the same name in the source and target project, but they are set to different types (e.g. String, Number, Selection List and so on). Therefore the default value as well as the acquisition rule can't be synchronized.
 

There is a Work History status in the target project which can be removed, because it doesn't exist in the source project. However, this status is used by at lease one drawing in the target project so it can't be removed.

If you want to have this status be removed from the target project, you have to check which drawings use this status and change the status to a different status. So the next time you run PlantSync this status can be removed.
 

AutoCAD Plant 3D doesn't allow deleting a Selection list which is already in use. So of course PlantSync doesn't allow removing a Selection list in the target project even though it's not used in the source project.

Here again, you would have to change the properties which use the Selection list which is supposed to be deleted.
 

The same explanation as mentioned above applies here too. Just in this case for Symbols.

This could be a little bit difficult to fix, because the symbol which is supposed to be deleted may be used multiple time in project drawings. So you would have to replace them.
 

If the attribute GraphicalStyleName is set to a symbol name which doesn't exist in the target project, the value for GraphicalStyleName can't be set.

You may want to consider selecting Add Symbols and Lines too so the value for the GraphicalStyleName can be set after all in the target project.
 

The same explanation as mentioned above for Selection lists applies here too. Just in this case for Tags.

Here you would have to change the symbols or lines to a different Tag in the target project so it can be removed.
 

In the source project the TagFormatName is set to a Tag which doesn't exist in the target project.

You may want to consider selecting Add Tags too so the missing Tag will be added to the target project too.