Nilfisk makes this kind of wye adapter for a host of different companies (including Festool). A simple google search provides different options:
https://www.google.com/search?client=firefox-b-1-m&biw=360&bih=512&tbm=isch&sa=1&q=Nilfisk+Bosch+splitter+y+tee&oq=Nilfisk+Bosch+splitter+y+tee&aqs=mobile-gws-lite..#imgrc=CCrVwyyhEWrhIM
Here's the Starmix-branded version:https://www.amazon.de/-/en/425689-starmix-DIY/dp/B005DERJJS?ref_=d6k_applink_bb_marketplace
And the Nilfisk-branded version:https://www.ultimategarage.com/shop/part.php?products_id=400
https://www.google.com/search?client=firefox-b-1-m&biw=360&bih=512&tbm=isch&sa=1&q=Nilfisk+Bosch+splitter+y+tee&oq=Nilfisk+Bosch+splitter+y+tee&aqs=mobile-gws-lite..#imgrc=CCrVwyyhEWrhIM
Here's the Starmix-branded version:https://www.amazon.de/-/en/425689-starmix-DIY/dp/B005DERJJS?ref_=d6k_applink_bb_marketplace
And the Nilfisk-branded version:https://www.ultimategarage.com/shop/part.php?products_id=400