Adding external site & keeping main menu

Hi!

I would like to keep our website’s menu (https://twogeeksonecup.com) on top of our forum (https://forum.twogeeksonecup.com) - even when people navigate directly to the forum instead of clicking on the link on our website’s menu.

Similar to https://forum.rocketbeans.tv/ (same menu than https://rocketbeans.tv).

I already tried adding a blank page + adding html (link) or an “External Site” element. But both variations won’t load my forum.. (plus afaik I would have 2 vertical scroll bars as I can’t have a dynamic page height in iframes, right?).

Any ideas?

Best,
Dan

PS: JESUS… the forum would not let me add my full domain.. pls replace .com with “.w t f” (withtout the space)