You've probably heard linking to other pages within your website provides SEO value, which is true. You should link to relevant pages within your website if it provides value to visitors, especially when the pages are deep within your website. Don't link to top level pages in the navigation menu, such as a link to your home page. Link to a short phrase which tells readers what the link contains; you don't have to use one of your keywords as the anchor text.
People have a tendency to want to keep visitors on their website, however, external links can also provide value to readers. Have the link open in a new tab and you won't lose the visitor. You can use to cite sources of statistics; it shows your website contains credible information. If your website is a resource guide, you must link to the websites you list as resources, otherwise, your resource guide isn't very helpful for visitors.
You shouldn't worry about the PageRank of an external link. You can only lose credibility by linking to undisclosed paid advertising or spammy websites. Good outbound links which provide value to your readers don't devalue your internal links.
It is possible to have too many outbound links. You don't want your website to look like a low-value directory. You can create a resource guide which won't look like a directory if you have original text describing each resource. You want to avoid too many disclosed affiliate links as well. It will annoy your visitors and tell search engines that your website does not have value.
Both internal and external links will add value to your website. If you can justify a link with adding value for your visitors, use it and don't worry about SEO. Additionally, you may find the more you link out to other websites, the more backlinks you'll naturally earn. For more information click here https://www.reddit.com/r/SEO/comments/bx4riw/doexternallinksdiminishvalueofinternal/.