I've noticed a few posts where people are asking for an alternative to BaseCamp Mac now that support for Apple Silicon doesn't seem to be forthcoming. The best I've found so far is the website GPX.Studio (https://gpx.studio).
I've been using it to create GPX files for biking and hiking routes that I can load on to my Garmin Oregon handheld (hiking) and Garmin Edge (biking).
For the Oregon I just export the GPX files from the gpx.studio app to the Mac file system and then copy them to the GPX folder on the Oregon using the macOS Finder.
For the Edge bike computer the exported GPX files are first uploaded to the Garmin Connect web site before being sent to the Edge.
The GPX.Studio app uses a few different basemap's including various versions of OpenStreetMap. It's very fast, unlike the dog that is BaseCamp, and fairly easy to use once you get a hang of it.
Hope this helps those of you looking for a BaseCamp alternative. Let me know if you have any alternatives that you found useful. I'm open to trying anything.