I was able to recreate this issue in my developer org. Here is what I did
Step 1: Went to Setup >> Survey Settings >> Enable Surveys and noticed that 'Select the default community for creating public survey invitations' does not have any values
Step 2: Checked list of all available communities from Setup >> All Communities and noticed that they are in Preview state
Step 3: Activated 'E-Bikes' community by clicking Workspaces > Administration
Step 4: Refreshed the survey settings page and observed that 'Select the default community for creating public survey invitations' shows the active community
Verified this in another developer org where I have enabled surveys already and observed that the list shows only active communities
Based on my observation, the only criteria for 'Select the default community for creating public survey invitations' to display results is that the community should be active. If the community is already active and does not show up in the list, I recommend raising a support case. Also, you might want to check if it is a site or community and ensure you are activating the community