Assuming I'm not the only non-zoomer remaining, if you remember /b/ from 2005-2009, it was not a porn-dumping board during that era, it actually had active admins and moderators like wtsnacks and moot who moderated the board and did "lulzy" things like banning OP's of threads who they thought weren't "funny." The problem with pornography-focused threads in unmoderated "general"/"off-topic" boards like /siberia/ is they spread quickly like fungal infections taking up all the focus away from other threads.
To save /siberia/ from this fate I suggest making a new board called /smut/, /lewd/ or /trash/ and moving all porn threads in /siberia/ to this new board. I'd also limit this new board to no more than 10 pages.
I also noticed you STILL haven't blocked images in
https://leftypol.org/robots.txt , you will inevitably get hit with google-image-bot-scouring copyright troll DMCA complaints from people making these porn dumps, and your web host OVH is known for eventually banning customers from their services after they get tired of receiving a high amount of DMCA complaints from their customers. You can block for just one board if you want, it's not rocket science, e.g.:
User-agent: *
Disallow: /boardname/src/
Disallow: /boardname/thumb/