I found this thread because I too host a vichan based imageboard that has the same problem.
This is my solution to the problem.
Change your instance-config.php to this.
It may be a bit much but it blocks a bunch of sus TLDs, all link shorteners that I could find, strange prefix letters like "t.badurl.ru", blocks spaced out characters "B a d u r l . ru" and a bit more.
Warning I coded this using AI, im not so good at coding.
// 1. DNS Blocklists (Standard Defense)
$config['dnsbl'][] = 'rbl.efnetrbl.org';
$config['dnsbl'][] = 'dnsbl-1.uceprotect.net';
$config['dnsbl'][] = 'dnsbl.dronebl.org';
$config['dnsbl'][] = 'torexit.dan.me.uk';
// 2. LAYER 1: Block known Link Shorteners (Surface Check)
$config['filters'][] = array(
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