Can't enable the PHP DOM extension

Question

I have a server that has PHP 7.4.3 installed, but it doesn't load PHP-DOM.

It's not listed in php -m or php -i, nor when I load PHP on a page.

Here's what I tried so far:

1. Ran sudo apt-get install php-xml several times, it installs without a problem and shows the newest version is already installed.

2. Ran sudo apt-get install php7.4-xml, it's unable to locate the package.

3. Added extension=dom.so to php.ini and checked for the --disable-dom flag (not found).

4. Restarted apache multiple times throughout this process.

How can I enable the PHP DOM extension?