Hi,
Thank you for your reply.
The output of the command is the following:
Interface Plug Slot Notes
avahi-observe mailspring:avahi-observe :avahi-observe -
browser-support mailspring:browser-support :browser-support -
content[gnome-42-2204] mailspring:gnome-42-2204 gnome-42-2204:gnome-42-2204 -
content[gtk-3-themes] mailspring:gtk-3-themes gtk-common-themes:gtk-3-themes -
content[icon-themes] mailspring:icon-themes gtk-common-themes:icon-themes -
content[sound-themes] mailspring:sound-themes gtk-common-themes:sound-themes -
cups-control mailspring:cups-control :cups-control -
desktop mailspring:desktop :desktop -
desktop-legacy mailspring:desktop-legacy :desktop-legacy -
gsettings mailspring:gsettings :gsettings -
home mailspring:home :home -
mount-observe mailspring:mount-observe - -
network mailspring:network :network -
network-bind mailspring:network-bind :network-bind -
network-observe mailspring:network-observe :network-observe -
opengl mailspring:opengl :opengl -
password-manager-service mailspring:password-manager-service :password-manager-service -
pulseaudio mailspring:pulseaudio :pulseaudio -
removable-media mailspring:removable-media :removable-media -
screen-inhibit-control mailspring:screen-inhibit-control :screen-inhibit-control -
unity7 mailspring:unity7 :unity7 -
wayland mailspring:wayland :wayland -
x11 mailspring:x11 :x11 -
So yes, it seems that the password manager is activated.
I exit from mailspring and re-enter it but now it says that all the accounts are not synchronized (both with mailspring and mailspring --password-store="gnome-libsecret").
After this, I reverted back to 1.11 as suggested by @jerjako and now everything works fine.
PS: I just realized that the tray icon on top bar does not show up for version 1.12 while this problem is not present in the 1.11 version.