Man pages matching name tcl_putenv in section 3tcl:

Tcl_PutEnv.3tcl.en	debian 10 / tcl8.6-doc
Tcl_PutEnv.3tcl.en	debian 11 / tcl8.6-doc
Tcl_PutEnv.3tcl.en	debian 12 / tcl8.6-doc