DVD and BDs can be burned straight from the timeline:
Though I haven't used this method for burning BDs, Vegas Pro's user manual suggests that the discs can be played back on a BD disc player or BD disc drive. Burns can be made to BD-R and BD-RE media. Menus aren't available but chapters can be created by using markers on the timeline.
Before buying Vegas Pro, why not install the free trial version so that you can test it for yourself. Please note that there is currently a 2-for-1 offer where you can get Vegas Pro 21 now and also get Vegas Pro 22 on its forthcoming release - all for $199 USD.
Isn't the maximum resolution for Blu-ray 1920x1080? At least that's the maximum resolution available in DVD Architect. So a 4K project will have to be rendered down to FHD.
Edit: Okay, so you are not playing a Blu-ray movie, you are playing a 4K movie burned onto a Blu-ray disc and playing it like you would play a file on a thumb drive? I just need a 4K disc player.
So a 4K project will have to be rendered down to FHD.
Yes, that is correct. The Render Parameters window that opens after clicking on Tools/Burn Disc/Blue-ray Disc provides a number of parameters, the following being an example:
Format choices are MPEG-2 and Sony AVC/MVC with 1440x and 1920x options for both NTSC and PAL.
If a DVD burn is chosen, then the format is MPEG-2 with 720x NTSC and PAL choices.