itcl3-dev binary package in Ubuntu Focal arm64

 [incr Tcl] (or itcl) is a popular object-oriented extension for the
 embeddable Tcl scripting language. The name is a play on C++, and
 itcl has a similar object model, including multiple inheritance and
 public and private classes and variables. Unlike most OOP extensions
 to Tcl, itcl is written in C for speed.
 .
 This package contains the headers and libraries needed to embed or
 add C extensions to itcl.

Source package