URGENT: I changed the primary domain for the Main store and now the Admin panel does not load at all (I get a 404)

Magento 2.4.2-p1
Smartwave Porto theme

We were running Magento 1.9.4 with 3 domains on www.domainOLDMagentoinstall.com:

www.domain1.com
www.domain2.com
www.domain3.com

We set up a new Magento 2.4.2-p1 on www.domainNEWMagentoinstall.com. I wanted to switch the first domain from old 1.9 Magento to the new today so I have done the following:

• In the new Admin panel of Magento 2 (www.domainNEWMagentoinstall.com/admin) I changed the base URL for Main store from https://www.domainNEWMagentoinstall.com TO https://www.domain1.com
• removed domain1.com from ‘Domains’ in Cpanel of the www.domainOLDMagentoinstall.com hosting account
• added domain1.com to ‘Domains’ in cPanel of the domainNEWMagentoinstall.com hosting account

Now www.domain1.com loads correctly the new Magento 2.4.2-p1 site (from the domainNEWMagentoinstall.com Magento install) but there is no way to access the Admin panel as both of the following:

domainNEWMagentoinstall.com/admin

and

domain1.com/admin

resolve to an Error 404 page.

How can this be fixed?

UPDATED on October 9th, 2021:

I tried to run the following:

php bin/magento setup:upgrade

php bin/magento setup:static-content:deploy -f

php bin/magento cache:clean

php bin/magento cache:flush

php bin/magento indexer:reindex

But it did not help.

I guess my problem is similar to this as my front page is broken as well:

Changed Base_Url and Now I am getting 404

I also deleted all the folders mentioned in that article. The only thing I was not able to do was the ‘dicompile’ command as it could not be found.

When I go to my phpMyAdmin and look for core_config_data – I changed:

   web/unsecure/base_url
    web/unsecure/base_url

Here is another article but I don’t think I have a wamp server:

magento 2 admin url not working and loaded frontend is all messy