is it possible to mention roles or people on a specified date in Discord?
Example of a command: .date 24/01/2022 19:00 @role and then the role will be mentioned on 24th of January at 19:00?
It's definitely possible.
You're going to want to utilize the datetime module (or whichever time module you prefer)
A couple things to consider:

Unless you go with a separate db, memory will be wiped any time the
bot is disconnected or restarted and your reminder countdown clock
process will stop.
If you go with a separate db, you're going to want to store the user
ID, channel ID, and datetime object from the command (so your bot
knows who to reply to, how to reply, and when)

I would explore a tasks.loop to check against the datetime column in the db every "x" seconds and if the current datetime == the reminder time datetime, then a message is sent to the user ID in the specified channel ID.
Mention people at a specified date Discord py