Are you 100 percent certain that the domain name wasn't registered before and then got on the blacklist because of prior misuse?
It's quite possible that the domain you chose was registered previously and dropped because the previous owner misused it and burned that domain. The .ONLINE extension has been around for several years now.
https://www.billhartzer.com - personal blog where I've been writing/posting for over 20 years. Tell me about your project/site/app/service and I'll write about it. Always looking for article ideas.
https://www.hartzerdomains.com - personal list of domain names I own, in case someone needs a domain name for a project.
It's quite possible that the domain you chose was registered previously and dropped because the previous owner misused it and burned that domain. The .ONLINE extension has been around for several years now.