FVWM: a problem of .login starting fvwm (migration suse-ubuntu)

I am migrating (actually, configuring a new PC) from opensuse 42.3 to 
xubuntu 20.04.3. In particular I would like to clone my fvwm configuration 
(since I have a screen of the same size), the one in 
http://sax.iasf-milano.inaf.it/~lucio/WWW/Opinions/window.html

What I am noticing (which is probably not directly related fvwm itself 
but to the way it is started with the X server) is that the fvwm session 
does not run my .login (I am since ages a tcsh user, so I have a .cshrc 
and a .login).    Such .login is executed correctly in a ssh session.

The .login has few items (a PATH setting, a font path xset +fp setting 
(plus other audio stuff so far commented out) which is conditional to a 
$?XSESSION_IS_UP, and a setenv of some locale like LC_TIME to en_US.UTF-8)

Apparently ALL of the .login is not executed

(not just the part relevant to XSESSION_IS_UP ...by the way what is the 
correct way in ubuntu to check I am in an X session ?)

I checked with ps -H the way fvwm is started

On suse

     1  1690 root       /usr/bin/sddm
  1690 17584 root         /usr/lib/sddm/sddm-helper ... --start fvwm --user lucio
17584 17586 lucio          /usr/bin/fvwm

On ubuntu

       1     977 root       /usr/sbin/lightdm
     977   34424 root         /usr/lib/xorg/Xorg -core :0 ...
     977   56656 root         lightdm --session-child 12 19
   56656   56682 lucio          fvwm2
   56682   56759 lucio            /usr/bin/ssh-agent /usr/bin/im-launch fvwm2

The difference between fvwm and fvwm2 is virtual. On suse /usr/bin/fvwm2 
is a link to fvwm. On ubuntu fvwm is a link to /etc/alternatives... which 
in turn is a link to /usr/bin/fvwm2.

Suse has fvwm 2.6.6 and ubuntu has 2.6.8

What is apparent is that somehow suse performs a "login with my shell" 
before starting fvwm (thus setting my environment) while ubuntu starts 
fvwm ignoring my login shell choices.

How can I either change this order, or instruct fvwm under ubuntu so that 
it sets up a basic environment which is then inherited by all child shells 
(in xterm, urxvt or whatever) ?

Thanks

-- 
Lucio Chiappetti - INAF/IASF - via Corti 12 - I-20133 Milano (Italy)
For more info : http://www.iasf-milano.inaf.it/~lucio/personal.html