For me all links open by default to a new tab. Not sure why it doens't to some people.
In any case, it has been covered:
https://wpforo.com/community/how-to-and-troubleshooting-2/links-open-in-new-tab/#post-32317
By default (without any plugins):
As you see above it opens to a new tab (same for you?).
The question is why it doesn't work in your setup. Have you tried the default theme for a while ? Any other plugin that could change the default link behavior in wpForo ?
Most urls are copy/pasted by members rather than typed in so no, it's not sorted at all and neither does that JS code posted in the other topic work.
Example 1: (straight paste - will not open in a new tab)
Example 2: (paste as plain text [control+shift+v] will open in a new tab)
Example 3: (typed url - will open in a new tab)
Not sure why this happens...
Also @hector i see here:
that probably you have modified some code ? Or use some plugin for rel no follow etc etc ? Can that be the cause ?