The SeaSucker Mini Bomber bike rack seems like a solid choice for the Tesla Model 3.
As reviewed, this bike rack retails for $440 and discount flat-rate ground shipping is only $7. It uses suction cups to attach to the Model 3's glass roof and includes a spare suction cup in case you have any issues. The reviewer begins with an unboxing, pointing out that the rack is light, packaged well (without any styrofoam), and comes with an easy checklist inside the box top. For those that need more detailed instructions, there's also the usual manual.
The rack only took about two minutes to put together. All that is required is a wrench. After that, you simply set it on the vehicle's roof, pump up the suction cups, and you're ready to roll. The rack fits two bikes and the weight capacity will be just fine for road bikes or mountain bikes. However, if you plan to use it for two larger bikes, you just have to assure that they are offset in such a way that the handlebars allow them both to fit properly.
Video Description via The Beet Sweets on YouTube:
SeaSucker Tesla Model 3 Bike Rack Review