I’m not sure I understand exactly what you mean. Should for example participant #1 (Cassandra) be matched with #2 (Alexander) and the email tell that Cassandra and Alexander is paired – and write the pairing info to both #1 and #2 so you can see it in the list?
If this is correct, should the pairing just look for the first unpaired participant so the participant #1 is unpaired until #2 registers and is paired with the first unpaired (#1) and #3 is unpaired until #4 registers and is paired with the first unpaired (#3)?
For my list, participants could be enrolling (creating a list item) throughout the month so ideally, we would pair them all randomly once per month; but I did not consider pairing automatically as they come in.
Sorry for the delay. It is possible to create this, but unfortunately I’m a bit busy and cannot help you right now, but I might be able to do it next week.
I guess a solution would be to create a script to put in a web part page where you can hit a button that gets all the list items from the list, randomly pairing them and then writing the pairing information to a second list were you keep track of the pairs. You can then use a workflow / flow sending out emails.
Let me know if you have any more details and I’ll estimate how much time this will take to make.