Can a crowdfunding portal "curate" opportunities or must they accept any company willing to list on their portal?

A platform can set parameters for the type of company and offering it will accept. And then it can (indeed, must) deny access if it believes there is potential for fraud or if the issuer has not complied with the regs. Put those together and most platforms have the ability to filter out the types of companies and offerings they don't want to host.