The address "domain.com/blog" gives a 404 error saying the page could not be found. The address "domain.com/blog/" opens but it does not open without the / sign at the end of the address. What can be done?

This is a plugin route issue - open index.php of the blog plugin and look for a route with only 'blog/' then change to 'blog'

That's it!

Thank you very much

Notification to the plugin creator

It depends if you want to have url ending with slash or not, based on that route may be changed.

When we type domain.com/blog, the blog section was not opening.

/public_html/oc-content/plugins/blog/index.php

edit:

48 :     osc_add_route('blg-home', 'blog', 'blog/',...........

'blog', when I deleted the / in it, it got fixed.
Now, whether I type domain.com/blog or domain.com/blog/, the blog section opens.