Why does the Page I want to tag not show up
Particular Pages can have a username with special characters that are not supported by the library that we use for mentions, which is why the Page does not show up when you try to tag it.
Firstly, if you are facing this issue with a Facebook Page, make sure that you are searching the Page by its name, not by the Username as the tag will not work. If that does not work either, follow the steps below.
Simply create a shortcode. This is also very helpful if you tag this page a lot.
Use (for example) the following Shortcode Name and Value:
Shortcode: TomsOfMaine
Value: @mention[Tom's of Maine](urn:li:organization:43420)
You can use Postman to get the Value.

Whenever you have to tag this Page, simply select the shortcode in your post and the page will be tagged.

Finally, when you Preview the post, you will see that the respective Page will be tagged.

To learn more about shortcodes, take a look at this article here.
Firstly, if you are facing this issue with a Facebook Page, make sure that you are searching the Page by its name, not by the Username as the tag will not work. If that does not work either, follow the steps below.
The way to tag this type of page would be:
Simply create a shortcode. This is also very helpful if you tag this page a lot.
Use (for example) the following Shortcode Name and Value:
Shortcode: TomsOfMaine
Value: @mention[Tom's of Maine](urn:li:organization:43420)
You can use Postman to get the Value.

Whenever you have to tag this Page, simply select the shortcode in your post and the page will be tagged.

Finally, when you Preview the post, you will see that the respective Page will be tagged.

To learn more about shortcodes, take a look at this article here.
Updated on: 10/01/2022
Thank you!