The virus is going to have an enormous impact on the mechanics of campaigning. Conventions as we know them will probably not occur. Large rallies will be out of the question. The battle will be fought on the internet and the airwaves. Who will be the chief beneficiary?
Trump is going to be the dominant story; not only does he have lots of money, but his response to the virus will make news every day, while Biden will struggle for earned media. That’s less of a problem than you might think. Biden is not a great campaigner, and Trump will be reinforcing his image of corruption, divisiveness, and incompetence for swing voters every day he’s on TV.
The bottom line is that Biden is running as the closest thing to a generic Democrat as you can find, and being less visible does not detract from that posture. Being generic worked in 2018; it made the election a referendum on Trump, which is exactly what the Democrats want. It can work again in 2020.