I have been a member of about a dozen different paddling clubs, mostly whitewater oriented, in at least six states that I can think of off the top of my head. I have also participated in group paddle events with various meet-up, adventure, and other informal groups as well and have served as a volunteer trip leader to run paddling trips on local creeks run by a Nature Preserve.
Different groups are as different as different can be. Most paddling clubs will make some type of attempt to judge the capabilities of participants when it comes to whitewater trips at least. Often this is based solely on information provided by the participant. But that info is not always accurate.
On more organized trips, the group usually has to adapt to the pace and capabilities of the least able paddler. This can sometimes be a problem. Sometimes the more capable, ambitious, adventurous become frustrated. It is pretty common with paddling clubs for members to sort themselves out after a couple of trips. Often a couple or handful of compatible paddlers will branch off on their own and start running their own small trips. Some people simply bridle at any sort of limitation whatsoever and find they are better off paddling on their own. Less capable participants may sense they are over their heads and drop out. I assume the same thing happens with various meet-up groups.
Day trips on rivers generally require some type of inter-person coordination and cooperation, such as agreeing to meet at a certain place at a certain time, organizing and running a shuttle, and usually a general agreement that trip members will assure that everyone gets off the river safely.
If you are looking at a particular group or event, I think the best thing you can do is give an honest appraisal of your experience, desires, and capabilities, assuming there is someone who is acting as trip leader or organizer. I have paddled with meet-up groups in which there were no restrictions on who showed up whatsoever. Anyone might turn up. I personally avoid those types of venues now.
I strongly suspect if you are patient you will be able to find another like-minded individual to paddle with, but it might not happen with your first attempt.