You have to do this in the settings of JEM.
Go to "Basic Settings" (Grundeinstellungen)
There you find the section "Event Handling" (Umgang mit abgelaufenen Veranstaltungen) with "Handle Old Events" (Alte Veranstaltungen) …
JEM 2.3.0 / JEM 2.3.0 with core mods (custom fields)
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In the settings you mentioned I choosed "Alte Veranstaltungen in den Papierkorb" (old events in the trash), but there is still the same result. I still see the old events in the simple list (browser cache was cleared before) .
Also the option "Alte Veranstaltungen archivieren" (archive old events) has the same result.
I didn't try "Alte Veranstaltungen löschen" (delte old events) because I don't want to delete the old events. Sometimes I use the old events as a template for new ones.