Yep. It's NOT possible to sign up OCI without a payment method now. I signed up late last month and observed the same.

Additionally, it's next to impossible to spin up a free instance even if you provision it under the limit. Every single availability zone in the U.S. have all been constantly "emitting out of capacity" errors for free tier resource allocation. Ironically, if you provisioning beyond the free tier, they are ALL success.

So it looks like Oracle shawdow banned the free tier (or only allow a fixed set of free tier resources that are completely saturated all the time (unless someone spin down their free tier instances).