Those two things are mutually exclusive. Any domains purchased using Cloudflare registrar must use Cloudflare nameservers.
6.1 in the Domain Registration Agreement states that you cannot change the nameservers:
6.1 Nameservers . Registrant agrees to use Cloudflare’s nameservers. REGISTRANT ACKNOWLEDGES AND AGREES THAT IT MAY NOT CHANGE THE NAMESERVERS ON THE REGISTRAR SERVICES, AND THAT IT MUST TRANSFER TO A THIRD PARTY REGISTRAR IF IT WISHES TO CHANGE NAMESERVERS.
You’ll either need to use Cloudflare’s DNS and get a list of the required records from your host, or transfer your domain elsewhere to change the nameservers.
Normally you would just enter the specific hostname records that your hosting provider gives you.
I initially added the domain as addon domain and redirected non www version (mysite . com) to the www version (www . mysite . com), meanwhile i only added A record for the non www version which then redirects to the www version and still doesn’t.
I fixed this by adding A record for the www version