This took as surprisingly long time but I managed to figure it out:
fieldset.bbp-form {
display: none;
}
.page-id-170 * fieldset.bbp-form {
display: block !important;
}
I know this hides all and only shows on page id 170, and this is the opposite of what I asked but it suits my needs.
An answer more accurate to the question would be:
fieldset.bbp-form {
display: block;
}
.page-id-170 * fieldset.bbp-form {
display: none !important;
}
For both examples you would replace .page-id-170 with .page-id-(your page id). A quick guide to finding the page id: https://www.competethemes.com/blog/find-page-id/