After previewing the form with "Тест" in "Page to be sent as a message" I don't see any sections in "Section of the page" pulldown. The page contains the following:
==Section1== Section1 ==Section2== Section2
MediaWiki 1.36.1, PHP 7.4.15 (cgi-fcgi), MySQL 5.7.28-log, ICU 60.2, Apache 2.4.29-1ubuntu4.16
Extensions: Echo – (1a15ef8), VisualEditor 0.1.2, MyVariables 3.5.1, NoTitle 0.4.0 (780dbb6), DynamicSidebar 1.1 (b2f3feb), Lockdown – (2409546), MassMessage0.4.0 (c9b6e87) 19:21, 22 July 2021