How do I delete my post from months ago and stop receiving emails from people about it
You cant delete it, but you can edit it.
The best way to handle it is to unsubscribe from that thread:
1) Go to that thread: https://community.roku.com/t5/Channel-Issues-Questions/Paramount-Plus-not-working/m-p/685698#M78051
2) Select the 3 dots in the upper right corner below the Roku banner, choose "Unsubscribe"