Mailbox Search still very slow when dealing with a big mailbox

Steps to reproduce

1. Configure a mailbox that has a sizeable number of messages in it
2. Search for any expression in "In Ordner suchen"
3. Immediate answer is "Keine Nachricht"
4. Wait Wait Wait .... messages will appear (search takes minutes, not seconds

Expected behavior

1. Do not state "Keine Nachricht" but something like "Searching..."
2. I should see first results in a second (like in my Thunderbird mail)

Actual behavior

As I mentioned and also mentioned in https://github.com/nextcloud/mail/issues/10503 before, search speed has not improved at all.
If I search using the global search, I get results a lot faster, but if I click on the search result and it takes me to Nextcloud Mail, I still have to wait minutes before it shows the email.
What can be done to improve this? It seems to be an issue for a while with different attempts to fix. For us it is now the number one issue with users complaining the mailbox search is not functioning.

Mail app version

5.6.9

Nextcloud version

31.0.7

Mailserver or service

Dovecot

Operating system

Debian

PHP engine version

None

Nextcloud memory caching

No response

Web server

None

Database

None

Additional info

As mentioned by another member, you cannot stop the search, it will continue in the background regardless if you cancelled and eventually freeze your Mail App (fix is to close the browser tab and open it again)

Start by reproducing the search with a large mailbox and compare the Mail app search with the faster global search path described in the issue. Investigate why results take minutes, why an immediate “Keine Nachricht” appears, and why cancelled searches continue; done means responsive progress, prompt initial results, and searches that stop when cancelled.