Once you gain a VCP it will not expire. Only the 2V0-21.20 exam is retiring, not the certification gained by taking the exam.
If you have more experience with vSphere 7 then I would recommend taking the exam based on that version. There is also more exam prep content and study guides available for the older exam - I particularly recommend the Official Study guide from VMware Press.
Once again, just to reinforce the point, If you become a VCP 7, your certification will not retire at the end of Jan 2024, only the exam will retire.
