The game in window mode fits on my monitor which is standard 1920x1080 without scrolling. On itch.io you need to scroll past my banner once, on my own website, there's no scrolling needed but I've also disabled full screen. On the longest side it is 800 which fits well into a height of 1080.
I designed the game to be played on mobile devices (it's published on Huawei App Gallery and at Amazon). That's why I have an odd portrait resolution (450 x 800). If I was designing it for PC I would've used different dimensions.
I suppose the other developers are creating their browser games using resolutions more suited to desktops that can resize based on desktop dimensions.
We can program the cameras to fit black bars and force a resolution when necessary. I didn't in this case, because the game was okay on all my test devices.