I don't know about the current website software, but a couple of times, when I was writing a much longer than normal response, I clicked 'post reply' and it came back and indicated it was too big...maybe it was 2000 words or something like that.
There's two ways to work around it.
Plan A: What I did was to immediately highlight everything I had written and do <cntl>C (windows) to copy it into the clipboard. I then opened up my word processor and did <cntl>V to paste it in there. I then did a quick 'save as' to make sure I didn't lose anything. Then it was back to the still-open post (leaving the word processor open just in case) to figure where the halfway mark would be, highlight from that point to the end, and do <cntl>X to cut it out. NOW click 'Post reply'. Then start a new reply, and the part you had just cut out, use <cntl>V to paste it in the new post, and post it.
Plan B: write the entire thing in your word processor, save it, then sign on the this site and first highlight and <cntl>C copy the top half, <cntl>V paste it into the first reply. Back in the word processor, highlight the 2nd half, copy it, paste it and post it. Done.
For what it's worth, I wrote an extremely lengthy response 2 weeks ago on another RR oriented web site comparing Lightroom Classic 2020 and Photoshop Elements 15 essential edits I use for slides and pictures. I figured I had to break it into 5 or 6 different posts to get it all in using about a page and a half as a 'cut point'. (I just checked, it was 14 typewritten single spaced pages in my word processor) Each break was conveniently where I could insert up to 3 images (their image max per post). I actually wrote and repeatedly revised that post over a period of about 2 weeks in my word processor while processing over 600 'family' slides for a friend. When I was done writing, I inserted a short dashed line with a notation which two before & after pictures I wanted to insert. Of course, I had copies of each of the to-be-inserted images in a temp folder in My Documents so I didn't have to waste time searching for them. When it was time to post my epistle, I simply copied and pasted one chunk at a time, added the two pictures, and posted. At last check, the thread had over 700 views.