The fact that I wasn't able to find a SysCTL.conf file with tweaks for whichever GOS device demonstrates my ignorance and lack of expertise, but I just can't help myself and not post common tweaks applied to SysCTL.conf files in routers for improved security and performance. I hope GOS either plans to include them or already includes them:
IPv4 Redirection and IP Anti-spoofing
net.ipv4.conf.all.accept_redirects=0
net.ipv4.conf.all.accept_source_route=0
net.ipv4.conf.all.secure_redirects=0
net.ipv4.conf.all.send_redirects=0
net.ipv4.conf.all.shared_media=0
net.ipv4.conf.all.rp_filter=1 (excellent for IP spoofing resistance, but NordVPN protocol requires value to be either 0 or 2 to work correctly with NordVPN's NordLynx WireGuard protocool)
ARP and ARP Anti-Spoofing
net.ipv4.conf.all.arp_announce=2 (or 1)
net.ipv4.conf.all.arp_filter=1 (or 2)
net.ipv4.conf.all.arp_ignore=2 (or 1)
net.ipv4.conf.all.drop_gratuitous_arp=1
net.ipv4.conf.all.proxy_arp=0
ICMP
net.ipv4.icmp_echo_ignore_all=1
net.ipv4.icmp_echo_ignore_broadcasts=1
net.ipv4.icmp_ignore_bogus_error_responses=1
net.ipv4.icmp_ratelimit=1
net.ipv4.icmp_ratemask=88089
Multicast
net.ipv4.conf.default.drop_unicast_in_l2_multicast=1
net.ipv4.igmp_link_local_mcast_reports=0
IPSec (WiFi Calling)
net.ipv4.conf.all.disable_policy=1 (can be used for a toggle to fully disable IPSec WiFi calling)
net.ipv4.conf.all.disable_xfrm=1 (can be used for a toggle to fuly disable IPSec WiFi calling)
Generic
fs.file-max=395955
fs.protected_hardlinks=1
fs.protected_symlinks=1
kernel.dmesg_restrict=1
kernel.kptr_restrict=1
kernel.panic=0
kernel.panic_on_oops=0
kernel.randomize_va_space=2
kernel.sysrq=0
net.core.default_qdisc=fq_codel
Other
net.ipv4.ip_forward_use_pmtu=0
net.ipv4.ip_local_port_range=1024 65534
net.ipv4.ip_no_pmtu_disc=2
net.ipv4.tcp_challenge_ack_limit=999999999
net.ipv4.tcp_dsack=0
net.ipv4.tcp_ecn=2
net.ipv4.tcp_ecn_fallback=1
net.ipv4.tcp_fack=0
net.ipv4.tcp_fastopen=3
net.ipv4.tcp_frto=0
net.ipv4.conf.all.ignore_routes_with_linkdown=1
net.ipv4.conf.all.log_martians=1
net.ipv4.tcp_moderate_rcvbuf=1
net.ipv4.tcp_mtu_probing=0
net.ipv4.tcp_no_metrics_save=1
net.ipv4.tcp_retries1=3
net.ipv4.tcp_retries2=8
net.ipv4.tcp_rfc1337=1
net.ipv4.tcp_sack=0
net.ipv4.tcp_slow_start_after_idle=0
net.ipv4.tcp_syn_retries=3
net.ipv4.tcp_synack_retries=2
net.ipv4.tcp_syncookies=1
net.ipv4.tcp_timestamps=0
net.ipv4.tcp_tw_reuse=1