Stop Calendar from changing time-zone
It's a bit of inconvenience of how Google Calendar uses time zones.
Here is a brief explanation of how it uses time zones:

How Calendar uses time zones
When you create an event, you'll see it in your local time zone. It
will also show up in the local time zones for anyone you invite, even
if they're in a different time zone.

Some workarounds:
1. Disable device time zone
When you travel to a different time zone, you can see your calendar in the local time.

Open the Google Calendar app .
In the top left, tap Menu .
At the bottom, tap Settings .
Tap General.
Tap Use device time zone on or off.


If &quot;Use device time zone&quot; is on, your time zone will update
automatically as you travel. If &quot;Use device time zone is off&quot;, you can
select a time zone from the drop-down menu.

2. Create an event in a different time zone
There is another workaround involving setting time zone for an individual event in Google Calendar.
For example, if you're going on a trip to Bahamas and want to make sure your 2 PM island tour shows up on your calendar correctly, you should choose the time zone for Bahamas while creating your event. i.e

Create an event

Open the Calendar app .
Tap Create .
Tap Event .
Start typing in a title for your event. You'll often see suggestions – choose one or keep typing.
Tap Done .
Edit event details like the date, location, time, event visibility, and who's invited. If you don't share your calendar, you
won't see visibility settings at all for your event.
Optional: If you have more than one calendar and want to change which one you're adding the event to, go to the top and tap the
calendar name.
Tap Save.


References

Google Calendar help: Change calendar time zone without changing event times
Google Calendar help: Create an event