I've found every calendar program, regardless of o/s, way too complicated. All I want from a calendar is the ability to enter an event, a date and if the event is permanent (eg birthdays). No times, no email invites, no nagging popups. I wrote my own in using Perl/Tk. When I logon, and there is something coming up in the next 7 days, it pops up. If nothing is happening, no popup. It's been running happily for about 10 years, on several different boxes. There are two files involved, the dates file and the program itself.
My box at home (core i3 3.5Ghz, 8GB RAM, rotational disk) boots from cold to login prompt in 54 seconds. That's running OpenSuse. Once I've logged it, the box fires off Firefox, Sypheed, my popup calendar and a script to tell me the backup which runs at shutdown works. 22 seconds later we're ready to go.
My work box, similar spec but running Windows 10 takes 2 1/2 minutes from cold to login. When I've logged in, it fires off Firefox and Outlook mail client and whatever group policy does. 90-100 seconds later, it's finished stuffing about (all the hourglasses have gone) and I can do work.
The lower spec'ed Windows 7 box I also have at work and use sometimes, boots quicker and logs in faster too. My employer also plonked a Mac on my desk. It's a i5 processor and boots and logs in faster than W10 but not as fast as my home Linux box.
I've found every calendar program, regardless of o/s, way too complicated. All I want from a calendar is the ability to enter an event, a date and if the event is permanent (eg birthdays). No times, no email invites, no nagging popups. I wrote my own in using Perl/Tk. When I logon, and there is something coming up in the next 7 days, it pops up. If nothing is happening, no popup. It's been running happily for about 10 years, on several different boxes. There are two files involved, the dates file and the program itself.