EDIT: EWS continues to be supported for on premises Exchange and is not scheduled for deprecation.
More limiting is that the current release doesn't support custom Office365 tenant IDs. So basically, unless you are using outlook.com this won't currently work yet. I'm lucky that my org hasn't disabled SMTP and IMAP, but it's been so slow lately...
This is Microsoft we're talking about here, so if its slated for removal in Oct '26, it will be put into LTS, and finally 'retired' (but operational) _starting_ around 2031.
Take the blog article for what you will. I have noticed in Office365, they tend to be less backward compatible than you would expect from Microsoft.
> Microsoft swears it's happening
My tiny company had an on prem Exchange, migrated from GroupWise, and is now cloudy. I did all the migrations myself.
I have left things with our MX records pointing to on prem (Exim + rspamd + stuff) and relaying to MS 365 and a few IMAP daemons. If MS take the piss with licensing costs, I'll simply relay elsewhere and drop them.
Then I'll migrate my customers away. It'll take a while but it is not insurmountable.
FWIW: I use Evolution on my Kubuntu based gear to access M365 email. Wifey rocks Arch and I've deployed Evo on KDE there too.