Elnadmin, EAP-RADIUS auth scheme just means you're using a radius server to authenticate your IKEv2 clients instead of using the pre-shared keys on IPSec pfsense tab.
Your initiator becomes a supplicant and will send authentication to your vpn server, which becomes a radius client that forwards the request to the radius server, that in turn will performs authentication.
I'm trying to explain it as simpler as i could in english, which is not my primary language, and i hope i understood correctly your issue. Think the RADIUS server as a sort of "authentication gateway" that receives the authentication requests from some devices (in your case the VPN server) and authenticates or redirects authentication to the right server accordingly (could be locally, against an LDAP server like a domain controller, or certificate based), and replies back with a YES or NO and eventually some other messages.
It's completely transparent to the device you're connecting with, which will use the authentication configured on the radius server itself. Depending on how you configure authentication on the radius server, you need to set up clients accordingly. If you're using certificates to authenticate clients you're likely to use EAP-TLS, if you use usernames and passwords, you're very likely to use EAP-MSCHAPv2.
All those protocols can be configured in the FreeRADIUS:EAP/EAP section in the package configuration section, it's up to you to decide which one.
The main advantage of using a RADIUS server instead of the internal database is that you can use the same authentication server for multiple devices, such as network devices (managed switches and routers which normally don't support more complex authentication schemes), VPN servers, 802.1x networks and well, you got the idea. It's a standard protocol for Authentication, authorization and (eventually) accounting.
EDIT: in your case, under mobile clients you must also select the radius server database. You can configure pfsense to use other databases for authentication under Settings / User Manager / Authentication Servers, then your vpn server to use EAP-RADIUS, and your radius server with the correct EAP authentication.
From the message you posted in your first post, it seems the IPSec server is not configured to accept EAP requests. What protocol do you have under the P1 auth method and under FREERADIUS/EAP?