You will need to experiment with priority.
add_filter(
'the_content',
function($content) {
return 'text-to-append' . $content;
},
10 // this is a priority number; 10 is default
);
The “10” is the default priority. I don’t know what number JetPack uses but your original code, without a priority, should run at “10” so I’d try “9”, or “8”. It should be possible to get your code to execute before JetPack’s code.