Power Automate flow which sends an e-mail notification the last working day of the month, except holidays.
Simple and quick to implement. Rady to use. Enjoy!
Assumptions:
- Monday is the first day of the week
- Saturday and Sundays are non-working days

If you want to contribute and make it even better (i.e. including holidays or set start weekday to different), use my GitHub repository.
Above is just s simple version of specific need in the following posts:
Flow Schedule - make flows run when you want - get more scheduling options
Find Days in a month and end of the month