That warning means your IP is suspicious on reddit, datacenter IPs can still be used just not dirty ones or widely known ones.
They have been doing this for a while now, just didn't look as fancy as now. Before it was a white page with "whoa there pardner" saying.
It started in the late 2023, but there was a loophole, you could use old.reddit without any restrictions, but as of late march this year they disabled that too.
On the bright side, they will never implement true KYC because that will destroy one of the biggest and unique features of reddit: anonymity.
Doing such will literally destroy 1/3 of their traffic if not more.
But they will absolutely become more strict in future for bots/spammers/advertisers probably.