You can disable AAAA records for your
You can disable AAAA records for your entire zone by modifying the IPv6 Compatibility Setting via the API (not possible to modify in the dash), but not for specific records on your zone.
CYou wouldn't be able to force back IPv6 on records by manually creating AAAA Records as far as I know, as that setting effects the Proxy IPs Cloudflare responds with, it doesn't care about your actual records
CUnless of course you made your records unproxied
CThere's no way to turn off IPv4 either, so at best you could have two zones (websites), one with IPv4 (IPv6 disabled), and the other with IPv4/IPv6 (hoping that browsers properly prefer IPv6)
CI don't think what you're trying to do will be possible without Enterprise, or just using some other public service to get the IPs for you. There was one hosted on Workers (CF was sponsoring it, so presumely Ent and such), I forget the name though
It's worth noting though that it doesn't matter what record you use when it is proxied. You could have an A/AAAA, or a CNAME. Cloudflare responds to DNS Queries with A/AAAA with its own IPs. You can use the API to disable the AAAA Records, but yea like you noticed you cannot disable IPv4 Records, so you just have to rely on clients preferring IPv6 by default (which most should, if they have it, especially browsers), and filtering out IPv4 results from the IPv6 endpoint
It's worth noting though that it doesn't matter what record you use when it is proxied. You could have an A/AAAA, or a CNAME. Cloudflare responds to DNS Queries with A/AAAA with its own IPs. You can use the API to disable the AAAA Records, but yea like you noticed you cannot disable IPv4 Records, so you just have to rely on clients preferring IPv6 by default (which most should, if they have it, especially browsers), and filtering out IPv4 results from the IPv6 endpoint