Is it possible to share a single survey with folks outside of my organization who do NOT have aArcGIS subscription ? Basically I am building a survey I need someone with my client's firm to complete but I don't want them to have access to all of my survey's.
if the requirement is for people to use your surveys without having an ArcGIS login, then your only choice will be to share your survey publicly. There are some details about this here: https://community.esri.com/groups/survey123/blog/2016/11/10/getting-started-with-public-surveys
Now, making a survey public does not mean that people will automatically discover all your surveys. Not at least from the Survey123 field app, from which they will only be able to open surveys for which their URL is well known.
Similarly, if people open your public survey from a web browser they do not necessarily will get to know other public surveys you may have.
For people to discover your Public Surveys they must explicitly go into ArcGIS.com and search for them.