The character limit for the cover page or Steps may have been exceeded.
If the character limit has been exceeded, you can Save draft but cannot Release.
Please check the following and try the Release operation again.
Check the character count
If the character count for the cover page or Steps exceeds the character limit displayed on the editing screen, please adjust the content.
Related:
What is the maximum number of characters that can be entered in a Title or description?
https://help.teachme.jp/hc/en-us/articles/900006444683
How are characters counted?
https://help.teachme.jp/hc/en-us/articles/10268480807961
Can I also edit in the mobile app a Manual that was saved as a Draft in the web Browser version with a character count exceeding the limit for Release?
https://help.teachme.jp/hc/en-us/articles/35795088098969