It should be possible to have both at once.
Let me know if you still can't find the mansion exploration activity in the field or sealed realm in the tale realms after exploring a bunch more - they shouldn't be too rare.
Thanks, looks like what I thought may have happened has happened.
There's a 'discoveredMansion' value near the start of save files; this can be swapped to false so the Explore the Mansion activity will generate again. The same applies to 'discoveredRealmOfHeroes' if the Realm of Heroes is missing.
If you'd like, I can do the edit for you; I'll just need to know which save.
I've modified the save and uploaded it here - https://mega.nz/file/uu4UlRqL#HJKzdA8afQemYj_GFD-e1aRWP3MRbjIeY0pn-FabhMg
It should be possible to find the Explore the Mansion activity now, let me know if it works :)