The company I just started working for is migrating from SP2019 to SPO, and one of the major hurdles to doing so is that they have an intranet blog type site, where all of the major departments post their updates. Everyone from the CEO on down has a blog that get's updated, in some cases pretty regularly, others are more quarterly.
The interesting thing about this is that every user on the system, (10,000+), when hired gets automatically registered via powershell for alerts on every one of these sites, (each blog is in a different site). If a user decides they don't want to get those alerts for that dept they can click on the unsubscribe button for each one they no longer want to receive.
So I'm trying to figure out how to convert this whole thing to SPO. I created the central blog, (I know, I hate calling it that also), and made it a hub site. I created new site collections called HRBlog, etc, and linked them to the hub site. I made all the news and events roll up to the hub site.
All that works fine, but the alerts thing has got me stumped. I can't see any way to configure alerts on these things like the HRBlog, (which is the only alert I still get on the current system). The business wants these alerts to continue, and I can't see any way to make that happen. I also can't see any way to forcibly subscribe every user to any/all alerts to begin with.
This blog site is a very central part of the company's communication plan with it's employees. Most of the 10,000+ business users in the company pay a LOT of attention to the alerts in their respective areas, (us IT geeks don't care :-), and they really want to get alerts on these posts.
If I can't figure out a way to duplicate this in SPO I think there's a real good chance the project is going to be put on hold.