"And you do introduce another iceberg: Tk and X-server."

I'm not sure what you mean. A daunting heap of problems in front of you; and an even greater mass, hidden from sight, waiting to sink your ship? :-)

I write a lot of Tk programs: many posted here; many more for personal use. I don't have any problems with the setup I described above.

I do have this file, in my home directory, which might help with some of your problems.

# .bash_vars

# To be sourced by .bash_profile.

# Use for potentially volatile environment variables.
# Saves having to make repeated edits to .bash_profile.
# Also, can be sourced independently.

set -a

# For X11
DISPLAY=:0
LIBGL_ALWAYS_INDIRECT=1

# ... irrelevant personal variables ...

# For Tk
XFT=1

# For Git
SSH_ASKPASS=

set +a
[download]

I meant whether an X-Server package needed to be additionally installed on the windows machine. I am not sure if Tk still needs it in Windows or now can use native widgets and wm-calls, and if that distinction is transparent.

For ActiveState Perl or Strawberry, you don't need it. For cygwin Perl, you do.
map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

It's been a while now, so I don't recall the exact specifics; however, I didn't need to do anything special.

The "Cygwin XLaunch" (and other X Server applications) were installed as part of the initial Cygwin setup; I did not need to specify anything in particular for X. There were no additional installation requirements that I needed to perform on the Win10 side; e.g. no extra downloads of libraries, no x_for_cygwin.msi (or similar) to run, etc.

Please note that I'm not trying to fiercely promote Cygwin; I just wanted to put your mind at ease if you do choose it. It does everything I need in both the professional and personal arenas. My preferences and requirements may not align with yours.

Another thing that could make a difference is the OS and hardware. I've specified Win10 throughout (it's 64-bit). Briefly, my basic hardware is: 6 core/12 logical 3.2GHz CPUs; 32GB RAM; RTX 2080 Ti GPU; 2 x 2TB SSDs. All my comments are based on this setup; depending on what you have available, YMMV.

— Ken