Summary of my perl5 (revision 5 version 34 subversion 1) configuration
+:
   
  Platform:
    osname=darwin
    osvers=22.3.0
    archname=darwin-thread-multi-2level
    uname='darwin venturaa.local 22.3.0 darwin kernel version 22.3.0: 
+mon jan 30 20:39:35 pst 2023; root:xnu-8792.81.3~2release_arm64_t8103
+ arm64 '
    config_args='-des -Dprefix=/opt/local -Dscriptdir=/opt/local/bin -
+Dvendorprefix=/opt/local -Dusemultiplicity=y -Dusethreads -Duseshrpli
+b -Dcc=/usr/bin/cc -Dman1ext=1pm -Dman3ext=3pm -Dinstallstyle=lib/per
+l5 -Dman1dir=/opt/local/share/man/man1p -Dman3dir=/opt/local/share/ma
+n/man3p -Dsitebin=/opt/local/libexec/perl5.34/sitebin -Dsiteman1dir=/
+opt/local/share/perl5.34/siteman/man1 -Dsiteman3dir=/opt/local/share/
+perl5.34/siteman/man3 -Dvendorbin=/opt/local/libexec/perl5.34 -Dvendo
+rman1dir=/opt/local/share/perl5.34/man/man1 -Dvendorman3dir=/opt/loca
+l/share/perl5.34/man/man3 -Dpager=/usr/bin/less -sR -Dperlpath=/opt/l
+ocal/bin/perl5.34 -Dstartperl=#!/opt/local/bin/perl5.34 -Acppflags=-I
+/opt/local/include  -Accflags=-pipe -Os   -Alddlflags=-L/opt/local/li
+b -Wl,-headerpad_max_install_names   -Aldflags=-L/opt/local/lib -Wl,-
+headerpad_max_install_names  '
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=define
    usemultiplicity=define
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
  Compiler:
    cc='/usr/bin/cc'
    ccflags ='-fno-common -DPERL_DARWIN  -pipe -Os   -fno-strict-alias
+ing -fstack-protector-strong -I/opt/local/include -DPERL_USE_SAFE_PUT
+ENV'
    optimize='-O3'
    cppflags='-I/opt/local/include  -fno-common -DPERL_DARWIN  -pipe -
+Os   -fno-strict-aliasing -fstack-protector-strong -I/opt/local/inclu
+de'
    ccversion=''
    gccversion='Apple LLVM 14.0.0 (clang-1400.0.29.202)'
    gccosandvers=''
    intsize=4
    longsize=8
    ptrsize=8
    doublesize=8
    byteorder=12345678
    doublekind=3
    d_longlong=define
    longlongsize=8
    d_longdbl=define
    longdblsize=8
    longdblkind=0
    ivtype='long'
    ivsize=8
    nvtype='double'
    nvsize=8
    Off_t='off_t'
    lseeksize=8
    alignbytes=8
    prototype=define
  Linker and Libraries:
    ld='/usr/bin/cc'
    ldflags ='  -L/opt/local/lib -Wl,-headerpad_max_install_names   -f
+stack-protector-strong'
    libpth=/opt/local/lib /Library/Developer/CommandLineTools/usr/lib/
+clang/14.0.0/lib /Library/Developer/CommandLineTools/SDKs/MacOSX13.1.
+sdk/usr/lib /Library/Developer/CommandLineTools/usr/lib /usr/lib
    libs=-lgdbm
    perllibs=
    libc=
    so=dylib
    useshrplib=true
    libperl=libperl.dylib
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=bundle
    d_dlsymun=undef
    ccdlflags=' '
    cccdlflags=' '
    lddlflags='  -bundle -undefined dynamic_lookup -L/opt/local/lib -W
+l,-headerpad_max_install_names   -fstack-protector-strong'
Characteristics of this binary (from libperl): 
  Compile-time options:
    HAS_TIMES
    MULTIPLICITY
    PERLIO_LAYERS
    PERL_COPY_ON_WRITE
    PERL_DONT_CREATE_GVSV
    PERL_IMPLICIT_CONTEXT
    PERL_MALLOC_WRAP
    PERL_OP_PARENT
    PERL_PRESERVE_IVUV
    PERL_USE_SAFE_PUTENV
    USE_64_BIT_ALL
    USE_64_BIT_INT
    USE_ITHREADS
    USE_LARGE_FILES
    USE_LOCALE
    USE_LOCALE_COLLATE
    USE_LOCALE_CTYPE
    USE_LOCALE_NUMERIC
    USE_LOCALE_TIME
    USE_PERLIO
    USE_PERL_ATOF
    USE_REENTRANT_API
    USE_THREAD_SAFE_LOCALE
  Built under darwin
  Compiled at Feb 24 2023 04:18:24
  @INC:
    /opt/local/lib/perl5/site_perl/5.34/darwin-thread-multi-2level
    /opt/local/lib/perl5/site_perl/5.34
    /opt/local/lib/perl5/vendor_perl/5.34/darwin-thread-multi-2level
    /opt/local/lib/perl5/vendor_perl/5.34
    /opt/local/lib/perl5/5.34/darwin-thread-multi-2level
    /opt/local/lib/perl5/5.34
[download]

I'm not really sure what to look for in this output...

I think the main thing is that we can now see that we're not dealing with an old perl, that PERL5OPT (and/or other perl-specific environment variables) have not been set, and that everything looks sane.
The main thing is that you look for a "standout" difference between that output and the output that you get.
If there's nothing to be seen there, as is apparently the case, then at least we know to look elsewhere.

AFAICS, the issue should be reproducible on the problem machine by running this script:

use warnings;
#use Tk;

print "result:\n";
$_A = '16.25'; # string, not number
$_V = '12.99'; # string, not number
$formula = 'sprintf("%.0f", ($_V * $_A))';
$_W = eval($formula);

print "$_V\n";
print "$_A\n";
print "$_W\n";
[download]

If that doesn't reproduce the problem, then I would begin reinstating bits of the original script to it (starting by commenting in the "use Tk;" line) until you hit the point where the problem does kick in.

It's an interesting one ... even if that simplified test script successfully demonstrates the bug, then there's still the question of "why and how ??".
But let's not get too far ahead of ourselves ;-)

UPDATE: If the script I provided did not tickle the bug, then how about this one that fully reinstates the Tk stuff:

use warnings;
use Tk;

my $mw=MainWindow->new();
$mw->Button(-text=>"   Test   ", -command=>sub{test()}, -font=>'Helvet
+ica 18 bold', -pady=>20)->pack();
MainLoop;

sub test {
  print "result:\n";
  $_A = '16.25'; # string, not number
  $_V = '12.99'; # string, not number
  $formula = 'sprintf("%.0f", ($_V * $_A))';
  $_W = eval($formula);

  print "$_V\n";
  print "$_A\n";
  print "$_W\n";
}
[download]


Cheers,
Rob

I will see if I can get that output but I haven't gotten any reply in almost a week to my last message ...

Yes, please do follow up here with any additional info that becomes available.
I find it interesting to understand how such weird behaviour, as you've described, becomes possible.
So far, I can't think of anything other than "use integer" or maybe some locale issue (both of which have already been mentioned).
But who knows what else there might be lurking about ;-)

Cheers,
Rob