Mutiny of my team

I am facing a rather serious situation at work:

I am a marketing manager in a biotech company with about 700 people, leading a team of 5 directs and my whole team (assistant to specialist level, aged early twenties to mid fifties) complained to HR about a variety of problems they allegedly have with my leadership.
Among others, my team complained about not doing „actual marketing work“, that too many tasks come up on short notice and that they have lost trust talking with me about these issues.
The last accusation is the most serious to me as I do have weekly O3s, a weekly staff meeting and an “open door policy” according to the trinity, so I would think enough opportunities to bring up any issues. I am continuously asking for feedback whether there is anything to improve with all of my directs.

Anyhow, the complaint ended up with our CEO (whom I report to directly) and he delegated a first meeting to be held to a senior department head involved in „internal development“.
The meeting was set up within 2 working days notice and included my whole team, this senior colleague and myself. The senior colleague was allegedly supposed to function as mediator.
I thought it was an awkward setup as all accusations of course appeared as being voiced by the complete team even though I think there were very nuanced things voiced affecting individual directs, which would have been way better discussed individually. I also suspect that two people staged the thing and sort of persuaded the others to join in. We left the meeting without any results.

My personal impression is that my team is overwhelmed with their work, in my opinion for lack of experience but also lack of work attitude. I covered for my team on numerous occasions, which might have been a grievous mistake looking back. The work is neither very easy nor too demanding but my very own complaint with every single member of my team and that I gave feedback about on multiple occasions is a perceived lack of willingness to think on their own, bring up own solutions to problems and not only asking for solutions. That was often received with push-back that I failed to address immediately.

So what I would like to know foremost for now is what to do in such a situation. There will be a meeting soon where potential solutions are supposed to be discussed.

I am definitely willing to improve. At the same time my directs need to improve and I am not sure whether they are willing to. I fear that the wrong things might be on the table due to my team running to HR behind my back.