So many comments debating the philosophy around this. I like it when these type of sites open a new tab for me. Is there a way to just code in a toggle between the two link opening types?

This is the type of thing I have to fight against daily. You already have both action available - left click or middle click. Don't bloat your software with band aids for problems that don't exist - just train your users better.

Middle-click a link to open a new tab. I can't force a link to open in the same window but I can with new tabs.

Sometimes it's easier to follow a link, have a look, and then go back without jumping around tabs.

I like that in Kagi I can set this as an option.

Default, on the same tab (since browsers have options around this), but allow users to select if they want it on a new tab/window.

You can set a user preference to open in a new tab. The reverse is not true.