Time zone support on Calendar gives variable results with .ics files, generates chaos in my schedule

I travel a lot between time zones for my work. I use Calendar v.14 and Fantastical 4.0 on OS Sonoma to try to keep my appointments, meetings, Zoom calls, flight itineraries, etc., to keep my life and work in order.

I make constant use of .ics files for flights, Zoom calls, and many other scheduling items, combined with "time sone support" turned on.

Yet some --not majority, yet still signficant percentage-- of items always get scheduled in the wrong time zones, throwing everything off and generating chaos. I always check to see that time zone support is still turned on (it is) and that my computer shows me to be in the correct time zone (usually, but not always it does; and the problem still occurs when it shows me to be in the correct time zone).

So why I am subjected to this chaos of some percent of my appointments always being scehduled at the wrong time?

Help please!