Best Calendar app?

[xka]

Can you recommend some calendar apps which support these features?
1. Different coloured events
2. Show multiple months in the left pane
3. Able to select arbitrary number of days for detailed view

I used Thunderbird with Calendar tweaks plugin, but it doesn't support #2 (at all) and #3 (only can select 1 week (7 days) or multiweek view starting with Monday for detailed view) and with the Calendar tweaks plugin becoming incompatible with latest Thunderbird I also lost #1

Are there any decent calendar apps on Linux, or do I have to go back to Outlook in a Windows VM?

[rossdv8]

Last month I replied to a similar question, because I was bored and curious.
Check whether an app called borgcalendar appears in your Software Manager.
It shows in mine, but I am not sure if that is simply because I have it installed.

A bit of searching my notes and it seems I grabbed it from Sourceforge:
https://sourceforge.net/projects/borg-calendar/

It is a Java app, so is self contained and should run on most versions of Mint (it does on the version of Java installed on my Mint 20.1)

After I submitted it as an answer to someone - I went on a strict diet preparatory to a colonoscopy. I set Borg calendar up to:
Open every day on startup and display on my desktop in Month view.
That gave me all things I had added over the current 30 days (suitably colour coded)
After I have seen it I can close it and it runs in the background

Pop up reminders on my desktop at timed intervals before (and after if needed) appointments / events.

It looks about as basic as you can get - but has a lot more going for it once you get inside.

On the other hand, everything I need to know is shown as soon as I boot up and at any time during the day by clicking it in the system tray.

It might not be as pretty as some - but since trying to help someone else with their calendar problem it has become my 'solution I never knew I needed'.
I did find some tutorial stuff somewhere - but just play with it and you'll soon find stuff.
Hint - double clicking on things sometimes does useful stuff. For example, double clicking on one of those squares in Month view opens up the window to add / edit events / appointments.

Hint - the row of icons goes Month View, Week View, day View and tools etc..

This might not be what you are looking for because I am not sure what you need here "2. Show multiple months in the left pane" but it might be worth investigating.
BTW, it has the option top store events in its internal database, and export them for backup - or to purge them if you don't want them on record.

[newlyminted7]

I tried all of them (there really should be more, and less buggy ones) and I went back to Evolution. It isn't perfect, but is about the best for what I needed. It may not do everything you want perfectly.