Google often crawls all the pages of the website no matter how we have linked it or not. However some of the times the bot from Google is so quick it may not track some of the new files. And in such case you can make use of the sitemaps as per the recommendation from the Google and other search engines. Here you can build sitemap.xml file and let the forum or blogs pages get indexed.
Keeping these things in mind, how do you create sitemap.xml for your blog?
Here is a good place to create a sitemap for your site: https://www.xml-sitemaps.com/
I've used it before and I must say that it's great for getting a sitemap for your site.
I feel like most of them have something built in. For Wordpress, I just use a popular plugin to build the sitemap. With forums, they generally have something included.