That's terrible – especially for the foreign YouTubers who relied on it, their audiences no doubt being crippled by this. YouTube’s tools weren’t very good, but they were better than nothing. At least it’s a good thing this forum exists (YouTube can’t take that away from us).
YouTube appears to be promoting Amara as an alternative for community subtitles (source):
QuoteWe are working with Amara to offer YouTube Creators a comprehensive alternative to our Community Contribution feature, which enables crowd sourced captions.
Amara has extensive experience working with creators to crowd-source captions and translations for their content and has built a streamlined integration with the YouTube platform that enables real-time updates to creator videos.
YouTube will be covering the cost of a 6 month subscription of Amara Community for all creators who have used the Community Contribution feature for at least 3 videos in the last 60 days (more details coming soon). We hope this helps support Creators during this transition, as well as benefit those who have been contributing captions (as this is a crowd sourced option). Creators who don’t qualify for the subsidy are still able and encouraged to use Amara’s tools, including their free subtitle editor.
(The privilege of having community subtitles now appears to cost the creator $12 per month.)
Really, it shouldn’t be too hard just to let another user other than the creator upload subtitles. Unfortunately, that’s impossible, so here we are. It might be possible to use the API for that purpose, though that might just be too much effort. Do let me know if that is possible in any way.