Funnily enough, I think the CVE they're saying it is is wrong? The link to the project zero itw tracking page is for CVE-2021-30858 which is an IndexDB UAF, which is a completely seperate bug; the MITRE tracking page for CVE-2021-30858 just has the boilerplate "a malicious page can cause an exploit" from Apple, and doesn't say if it's for the IndexDB or FontFaceCache bug, so I think the Jailbreak people are just confused on this one.
Funnily enough, I think the CVE they're saying it is is wrong? The link to the project zero itw tracking page is for CVE-2021-30858 which is an IndexDB UAF, which is a completely seperate bug; the MITRE tracking page for CVE-2021-30858 just has the boilerplate "a malicious page can cause an exploit" from Apple, and doesn't say if it's for the IndexDB or FontFaceCache bug, so I think the Jailbreak people are just confused on this one.