Linux get UTC offset from current (or other) timezones on given date and time

You can use the date command. You set the timezone and then specify the date and time. The command will return that time with the -03 or -04, so you will know if DST was in effect.

For example, for Chile/Continental:

Before DST change this year:

$ TZ=Chile/Continental date --date='2020-04-03 11:00 +00'
Fri Apr  3 11:00:00 -03 2020

After DST change this year:

$ TZ=Chile/Continental date --date='2020-04-06 11:00 +00'
Mon Apr  6 11:00:00 -04 2020

To undo that, just set TZ to UTC and change the offset:

$ TZ=UTC date --date='2020-04-03 11:00 -04'