Push Notification cert server broken for (old) MacOS Server?

A subsequent communication from Apple crushes my hopes for remediation:

Following our call, I reached out to a member of our engineering team for further insight into the macOS Profile Manager email notifications you’re receiving. After discussing the matter with him, I learned that macOS Profile Manager will no longer be supported by Apple moving forward. 

As a result, to continue managing your devices in the same manner, you will need to consider an alternative Mobile Device Management (MDM) solution from a third-party provider or from Apple known as Apple Business Essentials. There are several MDM solutions available, and I recommend evaluating key aspects such as hosting options and pricing to determine which is the best fit for your organization.

For guidance on selecting an MDM solution, I recommend reviewing the following resources:

Apple Platform Deployment User Guide

Introduction to Planning Your MDM Migration

While my team in Deployment Programs Support typically assists with Apple Business Manager account administration, I believe the best team to assist you further with this issue is Apple Business Support. You can reach them at 866-902-7144, Monday through Friday, from 8:00 a.m. to 8:00 p.m. CDT.

My response was:

This mission is creeping in a direction I really don't wish to explore. 

All I want to do is establish some simple shared calendars for my family on some server that isn't public. I should think something this simple would be possible without the necessary to forge an authoritarian empire controlling every iDevice owned by my family. 

If legacy support for Mac OS Server has degraded to a point where Apple can no longer provide this service, I'll just have to add a calendar server to our existing Linux web host machine. I'd like to do this within Apple offerings, but I can't afford to take on a new administrative nightmare that exceeds the benefit obtained.

Now my effort is currently stymied by the new Linux-based calendars being perfectly accessible by every Apple device in my family except one crucial MB Air that is maxed-out at Monterey.

I miss the days when Apple stuff "just worked."