Just to follow up on this, contributors to kbin investigated and found that startrek.website appears to block user agents that contain "curl" in it now.
works. kbin apparently sends User-Agent: Symfony HttpClient (Curl) in its requests for images, which is different than how it handles other fetch requests. they've made a PR to change kbin to send the user agent it uses elsewhere in those image requests https://codeberg.org/Kbin/kbin-core/pulls/1098 once that is approved / merged they should start working again as instances update. It'd be nice if, assuming this is all accurate, the block on curl could be removed so people don't have to wait for the PR / instances to update but I understand if that is difficult