I did several sessions in April and May, but two weekly D&D games crowded out Traveller, unfortunately. We used Roll20 along with Discord. Eventually Zoom pushed out Discord.
One interesting thing about Roll20: the virtual tabletop is great for adventure path games, where you more-or-less know what the players are doing in advance. They're exploring the sewers of Waterdeep, or venturing into the Wormcrawl Fissure, or fighting the dread pirates of Drinax. This gives you a chance to set up the maps and NPC tokens.
A sandbox game, and particularly a wide-area sandbox game like Traveller, is much much trickier to run on Roll20. The players might want to jump to the boring high-pop world you haven't fleshed out instead of the low-pop one full of animal encounters. You can roll with that easily enough in person, but it's a bit harder when you are "expected" to have audio/visuals prepared. In a pinch you can open up a blank hex or grid page on Roll20 and sketch stuff up, but you lose many benefits of the medium.
One solution would be to acquire a bunch of pre-made terrain pieces like "generic starship cargo bay" or "generic TSA hostel" or "warehouse." Just like it's handy to have a bunch of pre-made NPCs or patron encounters. Roll20 has great support for D&D and Pathfinder and fantasy games in general, but far less for sci-fi settings.
Another solution would be to just ignore the Roll20 and just go Theatre of the Mind for everything. I'd miss seeing the dice rolls, but that's ok.
