Still no joy trying to install Tk :P

Hi, all!
I’ve not looked at Ruby for a few years (busy-busy with that ‘real life’ rubbish!).
Anyway, I never was able to figure out how to get tk installed.
Try as I might and searching various sites, including this one, I just haven’t had any joy. I assume there’s something out there for this, but I’ve just not been able to find it as yet.
Anyone know how it can be done? I’ve tried gem install, apt-get install and all sorts of fun stuff, but still no luck.
If anyone could point me in the right direction, it would be much appreciated.

AND I should have said, I’m using antiX 23 (debian based).

I did also try to use $ sudo gem install tk and got this error message if it’s any help trying to figure out where I might be going amiss:

$ sudo gem install tk
Building native extensions. This could take a while...
ERROR:  Error installing tk:
	ERROR: Failed to build gem native extension.

    current directory: /var/lib/gems/3.1.0/gems/tk-0.5.1/ext/tk
/usr/bin/ruby3.1 -I /usr/lib/ruby/vendor_ruby -r ./siteconf20250312-21746-68s9an.rb extconf.rb
mkmf.rb can't find header files for ruby at /usr/lib/ruby/include/ruby.h

You might have to install separate package for the ruby development
environment, ruby-dev or ruby-devel for example.

extconf failed, exit code 1

Gem files will remain installed in /var/lib/gems/3.1.0/gems/tk-0.5.1 for inspection.
Results logged to /var/lib/gems/3.1.0/extensions/x86_64-linux/3.1.0/tk-0.5.1/gem_make.out

Thanks in advance!