SQL-DATABASE ERROR

Database error in WoltLab Burning Board (2.3.6): Invalid SQL: SELECT COUNT(articleid) FROM bb1_lexika WHERE visible = 1 AND catid IN (1,2,3) AND INSTR('',UCASE(LEFT(topic,1)))>0
mysql error: Illegal mix of collations (utf8mb4_general_ci,COERCIBLE) and (latin1_swedish_ci,IMPLICIT) for operation 'instr'
mysql error number: 1267
mysql version: 8.0.18
php version: 5.6.40-13+0~20191026.23+debian9~1.gbp37e45b
Date: 19.02.2020 @ 18:20
Script: /lex.php?action=letterlist&catid=0&letter=%C4%D6%DC
Referer: