User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:85.0) Gecko/20100101 Firefox/85.0

Steps to reproduce:

Get an invitation to an IT job application event.

My System:

uname -a
Linux anon-80hw 5.10.15-1-MANJARO #1 SMP PREEMPT Wed Feb 10 10:42:47 UTC 2021 x86_64 GNU/Linux

cat /etc/timezone
Europe/Berlin

Thunderbird 78.7.1 archlinux-1
Europe/Berlin

Actual results:

Get stunned why the time differs from the arrangement.

Ensure other recipients get the correct time. (The maybe-future-employer went a step further and even checked their [Windows,Exchange] settings.)

=> It must be on my side (client).

Check the HTML source of the e-mail. => It's binary base64 encoded.

It must be in preferences. But I already checked. Double-checked. This time also the calendar.

And there is the culprit. The timezone is wrong.

Expected results:

The timezone setting in Preferences -> Calendar should have been correct.

It was correct on system and in thunderbird. But not in calendar.