Are you using the Stable or Unstable repository? If you aren't sure, run eopkg lr in your terminal.

Here's the output:

user@pc ~ $ eopkg lr
Solus [active]
   https://mirrors.rit.edu/solus/packages/shannon/eopkg-index.xml.xz

Relevant bug report: https://gitlab.gnome.org/GNOME/evolution/-/issues/1969

@ZachBacon already updated Evolution to 3.46.0 which contains the fix for this issue. This will be resolved as of the next sync.

@ReillyBrogan , okay, nice. Thank you.

@poisey did the update work for you?

@ZachBacon my OS is fully updated but, no, the "New" button still doesn't work. Tried rebooting, too.

To whom it may concern: a workaround here is clicking on "Contacts" and then back on "Mail" in the left side-bar.

In T10405#198609, @ZachBacon wrote:

@poisey did the update work for you?

They're on Stable, so the update hasn't gone out yet.

In T10405#198611, @EbonJaeger wrote:

In T10405#198609, @ZachBacon wrote:

@poisey did the update work for you?

They're on Stable, so the update hasn't gone out yet.

That I'm painfully aware of now. I was gonna comment on that, but lost track of time.

@poisey The sync just happened this weekend, the updated evolution should be in now.

@ZachBacon, many thanks, with the new update it works again.