Changing this would probably mean that the active object should always to handled as selected in the context of this setting (so also for bones etc.). I'm not sure if there is any good reason for the current behavior. I agree it does make sense to show the active as well as the selected objects.

@William Reynish (billreynish), is there any reason for why the active object should not be handled as selected objects in this context?

Ooops, you were faster :D

There is one point here. The Dopesheet is reused for Annotations and this is not related to Active Object, so we need be careful about that.

Proposed fix (now when you enter in any mode, the object is always dsiplayed in Dopesheet):

diff --git a/source/blender/editors/animation/anim_filter.c b/source/blender/editors/animation/anim_filter.c
index 625a52fc800..5e0a4c70157 100644
--- a/source/blender/editors/animation/anim_filter.c
+++ b/source/blender/editors/animation/anim_filter.c
@@ -1830,12 +1830,13 @@ static size_t animdata_filter_gpencil(bAnimContext *ac,
         }
 
         /* check selection and object type filters */
-        if ((ads->filterflag & ADS_FILTER_ONLYSEL) &&
-            !((base->flag & BASE_SELECTED) /*|| (base == scene->basact)*/)) {
-          /* only selected should be shown */
-          continue;
+        if (ob->mode == OB_MODE_OBJECT) {
+          if ((ads->filterflag & ADS_FILTER_ONLYSEL) &&
+              !((base->flag & BASE_SELECTED) /*|| (base == scene->basact)*/)) {
+            /* only selected should be shown */
+            continue;
+          }
         }
-
         /* check if object belongs to the filtering group if option to filter
          * objects by the grouped status is on
          * - used to ease the process of doing multiple-character choreographies

I have seen the Active Onlyis implemented for Annotations mainly.

@Jacques Lucke (JacquesLucke) Do you agree with the proposed fix?

It does make sense. Two notes however:

• You should also update the comment.
• The commented out (base == scene->basact) seems to have solved the same problem. Either remove this code, or use it again.

This issue does not appear to be fixed in 2.93 or 3.0, so I'm going to re-open a new report.