Systemli's Matrix home server instance has a default retention time of 30 days. We allow values from 1-180 days.
It is possible to send custom events from developer tools of element web and set room retention time there. Something like: Right-click a room → Settings → Advanced → Open developer tools → Send custom event
You'll first need to convert the desired time in days to milliseconds, i.e.: 1000*60*60*24*<number_of_days>
type: m.room.retention content: { "max_lifetime": 34560000002 }
Click the red „Event“-button and then send.
After sending, you can verify that the retention is set: Go back and choose room state and m.room.retention there.
Source: https://github.com/vector-im/element-web/issues/3800#issuecomment-1030568445