Including subsections in ojs journals

Hi, everybody.
I expect you all to be safe.
My OJS journal “Historia Constitucional” has been modified to include “subsections”. That is a very important issue for us. For example, the main section “STUDIES” includes in each number different subsections depending on the submissions (for example: Spanish constitutionalism, XIXth century studies… and so).
I would thank to know if there is any plugin or way to include this option in latest OJS version. We are actually using a very old version because that modification we made, and any upgrade will destroy such modifications.
If there is no way to create subsections we possibly would leave OJS after 15 years working with it.
Thanks in advance for your kind help. Best regards.
PS: Actually our journal is not visible: that is a temporal problem as we are changing our University’s server. But we would like to take this opportunity to update OJS.