I only found a script that highlights the 3rd Friday of the month, which is not what I wanted.
This script tries to figure out the correct number of days per month but is not aware of holidays which might displace the expiry date.
This script tries to mark the last Friday of the month in the chart with a vertical line and/or a label.
It is meant for use on a daily BTC chart.
Price may tend toward a level known as the "max pain point" when options expire. See these articles:
Deribit is a place where you can trade BTC and ETH options. Monthly and quarterly options expiry
dates are relevant. From https://www.deribit.com/pages/informatio...
Daily options expire every day at 08:00 UTC.
Weekly options expire on each Friday of each week at 08.00 UTC.
Monthly options expire on the last Friday of each calendar month at 08.00 UTC.
Quarterly options expire on the last Friday of each calendar quarter at 08.00 UTC.