Hey there.
Here's a video of me making a test project and adding cls:0 to the first screen, and an image (in the same folder as the saved .tap file) in the second screen.
https://gyazo.com/39dfab84e3a3df80249dd2b493bf396f
The second video is the result running on ZXSP (I also tried it on Retro Visual Machine).
https://gyazo.com/f8decbd842087b1b50894628a743826f
You can see it's not working quite as expected!
I'm using an M4 MacBook Air and Safari version 26.3 - I've also tried ZXSF with Firefox, and on a PC with Firefox. Same result :(
Hope that helps, and any advice would be appreciated!
Cheers!
QS =D