MicrosoftDear BertJansen,
While I totally appreciate the need to sunset certain technologies, what Microsoft is doing to RERs is pretty catastrophic for quite a few business-critical applications I built for my clients. A significant factor of a smashing success Microsoft enjoyed with SharePoint was a very smart design allowing the platform to do all the heavy-lifting and leaving the finishing touches to developers. I help my clients to keep their special category personal data secure by instantly applying fine-tuned permissions using synchronous ItemAdded events on millions of documents and list items, there is absolutely no way webhooks or PowerAutomate Flows can be trusted with this sort of job. I see SteenWestergaard and Ward_Wilmsen are raising similar sort of concerns, and it's not just about performance. The key thing here is that synchronous event allow custom security to be applied before the new item form closes itself when saving, if the sensitive data is picked by the crawler in the period of time between the item being saved in the content database and webhook/Flow running, the sensitive data may appear in the search results for users who are not supposed to see it, and stay available like that until the next incremental crawl runs. While I understand the chances of that happening to a single list item are pretty slim, when there are hundreds of thousands of those for thousands of people the risk is getting real.
Synchronous ItemAdding evens also allows custom validation supported by a proper CSOM code which again is not going to be possible at all once RERs are killed. I don't mind learning some new tricks and technologies, but what Microsoft are doing here is extremely damaging as there are no alternatives to synchronous RERs provided whatsoever. The consequences of this retirement are severe and I don't want to recommend my clients to abandon Microsoft products if they want to keep their personnel records secure and sleep well at night.
