I tried to build it with the script but it failed saying I do not have a dependency installed, but when I checked synaptic I do have it installed. I however did run Icedove from the downloaded folder and set it up. It ran yahoo and google well, but the calendar was not there so I could not test that. I imagine the script would have built iceowl. I can not tell if it had integration with office 365. The dependency was autoconf2.13. Also after closing Icedove I noticed my CPU was high so I checked task manager, Icedove-uxp was taking a bit over 50%

@ Vanquishedangel - fun to know Icedove works for others!

1: you could build autoconf ver. 2.13 yourself, rename the executables to autoconf-2.13, autoreconf-2.13 etc. and copy the files into /usr/local/bin
2: the calendar (IceOwl) must be "switched on" under Tools => Add-ons => Extensions and Icedove rebooted for the calendar to take effect
3: on my laptop Icedove + Firefox + the Xfce desktop together according to Htop occupy 799Mb of memory
4: the TBsync extension will probably not work on Epyrus or Icedove as the extension is written for Thunderbird v. 60 or above, where UXP based apps only support extensions targeted at earlier versions

Thank you for feed-back! In fact I'm impressed you worked your way through the tedious manual set up of accounts. Regarding connectivity to cloud based calendars you could ask in the Epyrus forum, if such do exist?.

I also tried using davmail with epyrus and actually got far, but for some reason it is saying the password is wrong even though it is not. I may take a break then come back to it. But with davmail, all the clients should work with office 365.

Update, I got epyrus to work with Davmail and office 365. You need the newest davmail (not the one in the repos). The only downside is that when you link the calendar you have to create a new calendar and enter the url then authenticate, but all the calendars on office 365 link as one. This unfortunately will not work for me as I have staff reminders and other things I do not need notifications for. However we are a lot closer.

Update update: Claws-mail also works with davmail, however vcalendar plugin does not connect to office calendar

AlbusLuna's updated and patched uxp-browsers-230409.tar.bz2 bundle now give us athenian200's "Epyrus", New Toby Paradigm's "Interlink Mail" and Hyperbolas "Ice-Dove" email clients to build using the included script.
Earlier installments of the bundle might have had issues building on the most current Linux systems where i now just can confirm a test build of IceDove completed successfuly on a Linux OS coming with GCC 11.2.0 and glib 2.33 (Slackware 15).