Kiwifarms is definitely not pro-suicide. Some angrier members will hope their pet "lolcow" dies, and suicide is sometimes discussed when part of a newsworthy topic, but discussions on suicide methods are explicitly banned and the site owner has stated that it's not an appropriate forum to discuss them or suicidal ideation. Some members think freedom of autonomy dictates that people should be allowed to CTB if they choose, others think suicide is selfish/weak/dramatic, others just feel bad for people who CTB. YMMV, I'm not sure whether it's lifefuel or ropefuel not to read about all the people who live these batty, insane, degenerate, filthy, unstable lives and still have far more will to live than I do lmao.
It's tough to find other pro-suicide sites, not just because search engines deliberately refuse to index them, hard to find hosts, etc. but many smaller ones are also locked behind registration and verification to avoid negative press. I agree that antinatalists forums/subreddits tend to be pro-suicide but I find them a little whinier than places like SaSu and often more focused on hoping other people die/being bitter at people with happy lives than about CTB.
Depression forums on Reddit are hit-or-miss, some are touchy-feely pro-life and others validate or at least empathize with suicidal thoughts. You'll also find some NEET/Foreveralone forums that are quite frank about the likelihood of committing suicide once their parents or guardians die, whether because of no further support system, sadness, or just no longer having to live for anyone. Few methods to be found in these places though. Reddit even bans looking up the term CTB and just redirects you to a hotline resource.
Wish I could give concrete site names but they are elusive. I hear you though, I appreciate SaSu but I never like limiting myself to just one forum.