Just some additional information: I wasn't able to get any posts over 10k to actually go through, but once I edited them to be lower than 10k characters total, they showed up without issues. Seems like the current limit is still 10k, at least for text posts (but it would be awkward if comments were allowed to be 5x times longer than posts....)

An easy way to check for the length of what you're trying to post is to copy it to a text editor and let that program check for the number of characters. 10k is a LOT less than people assume.

(for comparison, this comment is already over 600 characters long.)

EDIT: Turns out that 10k is the initial limit for the first post / comment but once you edit it, the limit becomes 50k