Steven Sund implies that intelligence, with warnings, did exist and were available pre J6 but they were not acted upon.
It seems that advance requests for an extra National Guard presence (including from Sund himself) were denied and even calls for extra help were also delayed on the day, after the trouble had already started.
https://www.newsweek.com/ex-capitol-police-chief-sounds-alarm-jan-6-cover-1817365