Every modern OS, maybe with the exception of Microsoft Windows (but even they may have changed that meanwhile), “runs” on UTC (= system time) and local time is derived from that (where and when needed on the fly) with using time zone data. So users can’t set the tz for ROCK/Roon OS but the system could obtain that information automatically – but we don’t know for sure if it does because we don’t have access. Even if not, the Control could provide the tz or even potentially make the conversion (see also: Why UTC and not local time?[ticket in] - #2 by danny about backups).
No user, seeing terms like today, yesterday, … or a date, expects those to be expressed in UTC instead of local time. Please Roon Labs, fix that broken feature or remove it.