It’s possible to enable Google ReCaptcha or 2-step confirmation email for the JetPack contact form?
You can try https://www.ads-software.com/plugins/recaptcha-for-jetpack/, though it looks like that plugin is no longer being maintained. CAPTCHAs are also very hard for people with visual impairment to use, so I wouldn’t recommend adding that.
The Jetpack contact form is already being protected by Akismet,and if you’re getting spam submissions in the main feedback folder, just mark them as spam to train Akismet to start filtering them as well.
I’ve disabled many Jetpack modules.
They are quite and fully inactive or still using resources in the background?
If you’ve disabled a module, code for that module should not load when someone loads your site in their browser, and they shouldn’t use any resources.
The only exception I know of is the Image CDN – if you enable Tiled Galleries, it always uses the CDN even if the CDN is otherwise disabled. But the whole purpose of the CDN is to use our resources rather than your site’s.