So, I followed this thread and installed. The installation has worked and is noted that there was an upgrade from 1.15.0 to 1.16.0-5399a49f which I did and it has arrived back at exactly the same error message.
“Error: dlopen(/Applications/Mailspring.app/Contents/Resources/app.asar.unpacked/node_modules/better-sqlite3/build/Release/better_sqlite3.node, 0x0001): tried: ‘/Applications/Mailspring.app/Contents/Resources/app.asar.unpacked/node_modules/better-sqlite3/build/Release/better_sqlite3.node’ (mach-o file, but is an incompatible architecture (have (arm64), need (x86_64)))”
So I have Forced Quit and uninstalled using AppCleaner again. I would like to try the app again at some point, but I can’t use it if it is going to break and need to roll back to the previous version when that happens. I would have to check for feedback on the new version before upgrading. That makes things a little tricky…? It seems like a lightweight and useful product.