Hello,

Sorry to say but as far as we have preview your Site and Menu, the HTML Block is already selected and it is also previewing fine on your Site: https://snipboard.io/RmpNhE.jpg

So, we can’t seem to find any issues here.

Further, please remember to be able to select the HTML Block for the Menu Item, you need to first save the Menu after adding Menu Item then you could’ve the option to select the HTML Block for the Menu Items.

Best Regards