The provider is Weebly and requests will go direct to their Cloudflare account, but using a Worker requires the request to go through yours, hence the message which tells you that you can have one or the other, but not both.
Does Weebly offer a CNAME instead of IP address for their service? If so, try that instead and it may(*) work if compatible with their Cloudflare for SaaS setup. A Cloudflare-to-Cloudflare setup (known as Orange-to-Orange, O2O), can only be used with a CNAME, not A or AAAA records.
(*) “May” as they may have a legacy setup with Cloudflare where this is not possible.