I have a requirement for users to request their own sites and looking at a PowerApps front end tied to a list. Is it possible to use some form of Azure functionality such as Autosuggest or similar to suggest sites that already exist? Trying to prevent users from requesting the same site twice.
It's probably possible using graph to collect the sites and then apply a search to the collection in PowerApps, however, the issue you're going to run into is most of you're sites are probably set as Private, so the users wouldn't' be able to see those and they wouldn't return into your results.
You might be able to get around this by having a flow or something sync a site name list somewhere. But you'll need to consider the side effects of bringing in all private sites to be searched, if that could be an issue or not.
If you use a PowerApp and Flow, create a Flow that runs from the PowerApp that makes the Graph calls using an Azure App client ID and Secret so it runs as an admin context. As this will use the HTTP action you need P1 Flow licence for all users, alternatively create an Azure Function that you call from Flow as this does not need a licence but will incur Azure costs