We did get this working. However, as a mapping add in, it leaves a lot to be desired. It is very, very tricky to configure for use and requires a Site Collection Administrator to configure the tool for a SharePoint site. And that role needs to be explicitly granted to the user rather than applied using a security group. This certainly restricts it from general use within our SharePoint user community if it take a Site Collection Admin to add it to a SP site and configure it for use. Also, it doesn't seem to function very well in any browser other than Firefox. It just seems like the web part was developed in Classic and then modified for use in Modern(?) but the developers only tested it in Firefox. We use Enterprise logins which seems to just flummox it.
I also had difficulty using a Location field type within a SharePoint List to add data to the map. I think that may be a problem with Microsoft's support for Location fields rather than Esri. Microsoft seems to have pulled back that field type, at least if you are in GCC. The biggest deal breaker for us though with the ArcGIS Maps web part is you cannot label anything on the map. I don't remember the last time I created a map that didn't use some sort of labeling. Weird. This is ultimately the deal breaker that caused me to not use this web part at all.
There is also the ArcGIS Maps Search web part included with the product. Oddly enough, this web part DOES allow you to label data on the map. The drawback to using this web part is it displays the Geosearch dialog box on the left by default and there is no way to default the map to have that turned off on load. It also has a very different menu bar that allows you to do things like Geotagging and Geosearching which I also couldn't find a way to turn off by default. For just embedding a simple map inside a SharePoint site as a web part, it doesn't meet our needs either.
It almost seems like these two web parts were designed and created by different teams at Esri. They both look visually very different from each other. And they have different capabilities and configuration steps.
Frankly, to get a simple map embedded within a SharePoint site, it turns out to just be easiest to create it in ArcGIS Online and use the SharePoint </> Embed web part to put the published map onto your web page. This product just has the feel of being a side project at Esri. It isn't even listed in their Product directory like ArcGIS Maps for Office or ArcGIS Maps for Power BI.