Interestingly, it is seemingly working in 2.4.4-RELEASE. /var/etc/ipsec/ipsec.conf included for your entertainment:
P1 has AES-128-GCM and AES-256 (because Windows doesn't like my proposal for some reasons).
# This file is automatically generated. Do not edit
config setup
uniqueids = yes
strictcrlpolicy = yes
conn con-mobile
fragmentation = yes
keyexchange = ikev2
reauth = yes
forceencaps = no
mobike = yes
rekey = yes
installpolicy = yes
type = tunnel
dpdaction = clear
dpddelay = 30s
dpdtimeout = 120s
auto = add
left = [redacted]
right = %any
leftid = fqdn:[redacted]
ikelifetime = 28800s
lifetime = 3600s
rightsourceip = [redacted]
rightdns = [redacted]
ike = aes128gcm128-sha256-ecp256,aes256-sha256-ecp256!
esp = aes128gcm128-sha256-ecp256,aes128gcm128-sha256-ecp256!
eap_identity=%identity
leftauth=pubkey
rightauth=eap-tls
leftcert=/var/etc/ipsec/ipsec.d/certs/cert-1.crt
leftsendcert=always
rightca=[redacted]
leftsubnet = 2000::/3,0.0.0.0/0
System:
CPU Type Intel(R) Xeon(R) CPU E3-1271 v3 @ 3.60GHz
Current: 3600 MHz, Max: 3601 MHz
4 CPUs: 1 package(s) x 4 core(s)
AES-NI CPU Crypto: Yes (active)
Hardware crypto AES-CBC,AES-XTS,AES-GCM,AES-ICM
Kernel PTI Enabled
Tested on iOS 12.0.1/macOS 10.13.6, Windows 10 Pro for Workstations, no problems.
Windows configuration for those who are unhinged:
Set-VpnConnectionIPsecConfiguration -ConnectionName "ikev2" -AuthenticationTransformConstants GCMAES128 -CipherTransformConstants GCMAES128 -IntegrityCheckMethod SHA256 -EncryptionMethod AES256 -DHGroup ECP256 -PfsGroup ECP256 -PassThru