Simon 5 is coming soon!
Simon version 5 is currently in beta testing. It is a massive update, introducing a much-requested feature: syncing the Simon data between multiple Macs, plus a Simon Status service, a Link Checker filter, improved Find filter, iMessage and Speak Error notifiers, a new app icon, and much more.
Important: please note that Simon 5 requires a minimum of macOS 10.12 (Sierra), and will be a paid upgrade from Simon 4 after the beta. Purchasers since September 1, 2020 automatically get a version 5 license (that also works in previous versions).
Re: Twitter account not detected by Simon
This is a known bug in El Capitan (Apple bug tracker radar #23114308, #22869649, #22869928): discussion).
If you're able to use Yosemite, you should be able to set it up there.
I've tried several times to get Apple to fix this issue, but no luck. It affects all apps that need to access the accounts API. Very annoying.
Re: Twitter account not detected by Simon
Ya it would be nice to have a fix for this