It seems that posts on Lemmy cannot exceed 10000 characters. If you type in more than 10000 characters and try to submit the post, you will see that the post submission is being processed but you won’t come any further than that. The post submission will remain in status pending indefinitely.
This pull request will hopefully increase it to 50k. We just have to wait for instances to be updated to the lastest release https://github.com/LemmyNet/lemmy/pull/3263
Fsck me I love FOSS sometimes!