I can edit MX records but can't see "Connect an email purchased outside of Wix" button

Question:
Why am I not seeing the option Connect an email purchased outside of Wix

Product:
Wix Studio Editor

What are you trying to achieve:
I connected my domain using the “name servers” method. I would like to connect my existing corporate mailbox. However, there is no such item on the menu.

I requested the information from my provider. They gave me the necessary DNS records, which I entered into the domain settings in wix. I used my domain checker at https://www.whatsmydns.net/ The site shows the same DNS records as in the domain settings in wix. The only exception is a group of TXT records. The check sees the record “v=spf1 a mx …”, but does not see the second record “v=DKIM1; k=rsa…”.

I used https://mxtoolbox.com/ tool.
a test: Your DNS hosting provider is “Wixpress Ltd.” and list of 3 IP addresses.
mx test: IP address of my provider, DNS Record found, No DMARC Record found, DMARC Quarantine/Reject policy not enabled.
txt test: DNS Record found, “v=spf1 a mx include:spf.” record. But no second record.

In Wix the domain is listed as connected. My provider says that everything is fine on their end. Moreover, after switching DNS, the mail client connects to the mailbox again without any problems (the connection was interrupted for several hours during the DNS change).

Could you give me some ideas on where to look for the problem? At least which side.