Here’s my take on this. I can see why you’d want a way to recover that information, especially for event planning.
There are generally two approaches here, each with its own set of considerations. The first is using a server-side logging bot. If you have administrative permissions on the server, you could install a bot like Dyno or YAGPDB. These can be configured to log all deleted messages in a private channel for moderators. The major limitation is that this method is not retroactive; it will only work for messages deleted after the bot is configured.
The second approach involves client-side modifications like BetterDiscord, which allow plugins that can cache messages. However, using modified clients is against Discord’s Terms of Service and can pose a risk to your account’s safety. It’s a trade-off between getting the functionality you want and adhering to the platform’s rules.