How to add wildcard alias?

After adding wildcard mx. I want to add wildcard alias.
like any email (ex: XXXX@*.mydomain.com) to a single email me@mydomain.com

** I want to receive nay mailbox of any subdomain in a single mailbox. Is it possible? Then how?

No one here to help me?

Your request is a rather obscure one, so my suggestion is to experiment and see through trial and error if this works or not.
I use external DNS and my DNS provider does not allow me to set a ;wildcard’ subdomain MX record. Maybe yours does? Though I doubt it.
I experimented a little bit and discovered that there is no problem creating a catch all for a single subdomain in the alias section but not for a ‘wildcard’ sub domain.
So you may need to narrow your requirements to subdomains that you specifically create a catch all address for.

But I don’t want to create specific subdomain. Any incoming mail towards @.mydomain.com I want to receive it into me@mydomain.com

So just to make sure I’m understanding what you are asking.

You want something like
address@domain.com
address@domain2.com
address@subdomain.domain.com
address2@subdomain2.domain.com

To all go to one address. Is that correct?

If that’s what you’re asking, then I think what you’re looking for is domain aliases under the alias tab.

If you are just looking to do all the mail for a single domain (@domain.com), you would set a catch-all in the same section.

Note that both of these are designed to handle mail that comes to the domain but doesn’t have a known address. So for example, if you have an alias sending everything to alias@domain.com and an address me@domain.com, you would receive mail to me@domain.com if it is specifically addressed to that, all other mail would go to alias@domain.com

As I stated, a catch-all needs to be created for each subdomain. Having a catch-all for @domain.com will only forward email addressed to anything@domain.com. If you want to have a catch-all for any subdomain, you need to set a catch-all up for that subdomain. For example, anything@subdomain.domain.com needs a catch-all set up for @subdomain.domain.com, and so on.

MiaB will not allow you to enter *.domain.com as the catch-all alias. I tried it.

It does not appear that what you want to accomplish is supported by MiaB out of the box. You may be able to do so within postfix, but that would be an unsupported modification. This comment is based upon your op, not the comment I quoted as you did not include the * in that comment.