Does the Dryatek 2830 with Firmware 3.8.8.3 support IKEv2?
I can not see anything about it in the history of the firmware release notes.

According to this page: https://www.draytek.com/en/faq/faq-vpn/vpn.lan-to-lan/vigor-router-to-vigor-router-ikev2/
All firmwares from 3.8.5 onwards should support it.

I think that’s a typo from Draytek. The 2830 is a legacy product now, the 3.8.x fw was released for that model to simply mitigate the management vulnerability earlier in 2018.