This "missing contacts" problem has been around for many months, and I'm not sure there is a solid fix available. I happened across a potential temporary solution, or maybe it'll trigger someone's memory of a setting somewhere. I've described it in my post of November 14, 2024 with my name JerryAbrams. Here's the gist of what I did.
Situation: Outlook (new) Contacts do not appear, except when you do a search. This indicates to me that they are just being hidden. For example, in Contacts, Search for "@" and you'll see all your contacts that have an @ in their email address. So we have some hidden data to find.
Hopefully, you have a free copy of Office 365 where your contacts are visible. If so, in Office 365 Outlook, go to Manage Contacts, and export your contacts to create a CSV file. Then, in your Outlook (new), in Manage Contacts do an "import" contacts. In my case all my contacts suddenly appeared. In fact, each contact was duplicated the number of times I tried to export and immediately import. I didn't help myself, since 13 copies of each contact make it pretty unusable.
I suppose it's possible to start with some other version of Contacts, such as Office 2016 and import those contacts into Outlook (new). I hope this gets fixed sometime soon!