Seems like the linked repo name was changed and the link on this repo's readme never got updated.
EDIT: It looks like this repository is dead due to an official Bash release of SpotX.
Here's the official version, use this instead: https://github.com/SpotX-Official/SpotX-Bash
When clicking the 'experimental features' hyperlink listed under 'Features' it links to the following dead page: https://github.com/SpotX-CLI/SpotX-Win/discussions/50
I played around with the URL and got redirected to this link which seems to be the actual intended page: https://github.com/SpotX-CLI/SpotX/discussions/50
Seems like the linked repo name was changed and the link on this repo's readme never got updated.
EDIT: It looks like this repository is dead due to an official Bash release of SpotX. Here's the official version, use this instead: https://github.com/SpotX-Official/SpotX-Bash