I just added this page:https://gametz.com/OffSiteNotifications.html
If you click the "enable" button near the top, it will pop-up and you can then click "Allow. Then it should start sending notifications to the web browser you did that with. You can set it up for more than one browser, if you like. These are similar to app notifications, if you're familiar with that. I'm using the same system as I use for the Android app (Firebase Cloud Messaging or FCM).
The page also lists all the offsite notifications the sites knows about for you, including if you have an app setup to send notifications (e.g. Android or iOS). It calls browser notifications "Web Push" in that list.
There's also a Test button at the bottom that tries to send a test message to all the listed "Existing Offsite Notifications". Note that this doesn't seem to always work and it will open a new tab to your user page to do it because there's an odd quirk that prevents notifications from happening when the page that initiated them is in focus. It will also send the test to your phone if you have the app setup for that.
Consider this experimental and somewhat flaky. I was happy to get something working, but I'm finding it doesn't work so well. For example, the notifications only happen if your browser is running. So, it's not as thorough as the app tends to be with a phone. If your computer is off/sleeping, you'll never see a notification. That's intended behavior as far as I can tell. There doesn't seem to be a queue. The docs for this seem to be in flux, so it's really hard to tell what's going on. Most stuff seems out-of-date, etc.
I've tested it with Win10/Chrome, Win10/FireFox, Chromebook, and it even worked with chrome on my Android phone. It did not work for ios/Chrome (notifications are not supported there).
Let me know how it goes... if it doesn't work, there may not be much I can do about it. But, I'll listen.