You may want to take a look at this KB article: https://portal.smartertools.com/kb/a3747/autodiscover-dns-records.aspx

We've seen issues where Outlook attempts to autodiscover from Microsoft Cloud IPs, since that's what it connects to first, and it looks for specific connections. We've found that the autodiscover records listed for Outlook 2024+ seem to resolve this issue. 

Autodiscover works much better if you use registry keys on the client to limit the process to less than all 7 of tits available techniques.   This presumes that you can deploy registry keys to most users via group policy.   Here is a post that I wrote on the subject several years ago.   It is unfortunate that the substance of it was not added to the KB article mentioned by Derek.