combine registered var

I use ansible with win_updates to install windows update.
To get all updates installed I do multiple loops with a reboot in it
I do set the contents in a register.
But a reboot overwrites the register

How can I the register vars from multiple time to one var.
The contents is a dic
I tried something like this

my_strings: “{{ my_strings | default({‘key’:‘value’}) | combine(available_updates.filtered_updates, list_merge=‘append’) }}”

But I have one result in it