“this.activateMode is not a function” is the error message.
This is a known dependency issue normally solved by correct packaging of the plugin:
https://wpdevelopment.courses/articles/how-to-fix-activatemode-is-not-a-function-error-in-gutenberg/
I did some additional troubleshooting, and it looks like maybe it is your Starter Templates that are causing the issue as opposed to Spectra.
Deactivating it solves the issue for me, but I hope you can find the issue in your Starter Templates plugin.
