\K not permitted in lookahead/lookbehind in regex

use v5.32.0;
qr/(?=(?=x)x)\K/;

Summary of my perl5 (revision 5 version 32 subversion 0) configuration:
   
  Platform:
    osname=darwin
    osvers=18.7.0
    archname=darwin-2level
    uname='darwin daneel.local 18.7.0 darwin kernel version 18.7.0: mon apr 27 20:09:39 pdt 2020; root:xnu-4903.278.35~1release_x86_64 x86_64 '
    config_args='-de -Dprefix=/Users/damian/perl5/perlbrew/perls/perl-5.32.0 -Aeval:scriptdir=/Users/damian/perl5/perlbrew/perls/perl-5.32.0/bin'
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=undef
    usemultiplicity=undef
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
    bincompat5005=undef
  Compiler:
    cc='cc'
    ccflags ='-fno-common -DPERL_DARWIN -mmacosx-version-min=10.14 -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -DPERL_USE_SAFE_PUTENV'
    optimize='-O3'
    cppflags='-fno-common -DPERL_DARWIN -mmacosx-version-min=10.14 -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
    ccversion=''
    gccversion='4.2.1 Compatible Apple LLVM 11.0.0 (clang-1100.0.33.8)'
    gccosandvers=''
    intsize=4
    longsize=8
    ptrsize=8
    doublesize=8
    byteorder=12345678
    doublekind=3
    d_longlong=define
    longlongsize=8
    d_longdbl=define
    longdblsize=16
    longdblkind=3
    ivtype='long'
    ivsize=8
    nvtype='double'
    nvsize=8
    Off_t='off_t'
    lseeksize=8
    alignbytes=8
    prototype=define
  Linker and Libraries:
    ld='cc'
    ldflags =' -mmacosx-version-min=10.14 -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/11.0.0/lib /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/lib /usr/lib
    libs=-lpthread -lgdbm -ldbm -ldl -lm -lutil -lc
    perllibs=-lpthread -ldl -lm -lutil -lc
    libc=
    so=dylib
    useshrplib=false
    libperl=libperl.a
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=bundle
    d_dlsymun=undef
    ccdlflags=' '
    cccdlflags=' '
    lddlflags=' -mmacosx-version-min=10.14 -bundle -undefined dynamic_lookup -L/usr/local/lib -fstack-protector-strong'
Characteristics of this binary (from libperl): 
  Compile-time options:
    HAS_TIMES
    PERLIO_LAYERS
    PERL_COPY_ON_WRITE
    PERL_DONT_CREATE_GVSV
    PERL_MALLOC_WRAP
    PERL_OP_PARENT
    PERL_PRESERVE_IVUV
    PERL_USE_SAFE_PUTENV
    USE_64_BIT_ALL
    USE_64_BIT_INT
    USE_LARGE_FILES
    USE_LOCALE
    USE_LOCALE_COLLATE
    USE_LOCALE_CTYPE
    USE_LOCALE_NUMERIC
    USE_LOCALE_TIME
    USE_PERLIO
    USE_PERL_ATOF
  Built under darwin
  Compiled at Jun 27 2020 22:49:58
  %ENV:
    PERL5LIB="./lib:/Users/damian/perl5/perlbrew/perls/perl-5.32.0/lib/perl5/darwin-thread-multi-2level/:/Users/damian/perl5/perlbrew/perls/perl-5.32.0/lib/perl5/darwin-2level/:/Users/damian/perl5/perlbrew/perls/perl-5.32.0/lib/perl5:/Users/damian/perl5/perlbrew/perls/perl-5.32.0/lib"
    PERL6LIB="./lib6:/Users/damian/lib/perl6"
    PERLBREW_CSHRC_VERSION="0.76"
    PERLBREW_HOME="/Users/damian/.perlbrew"
    PERLBREW_MANPATH="/Users/damian/perl5/perlbrew/perls/perl-5.32.0/man"
    PERLBREW_PATH="/Users/damian/perl5/perlbrew/bin:/Users/damian/perl5/perlbrew/perls/perl-5.32.0/bin"
    PERLBREW_PERL="perl-5.32.0"
    PERLBREW_ROOT="/Users/damian/perl5/perlbrew"
    PERLBREW_VERSION="0.76"
    PERL_MB_OPT="--install_base /Users/damian/perl5/perlbrew/perls/perl-5.32.0/"
    PERL_MM_OPT="INSTALL_BASE=/Users/damian/perl5/perlbrew/perls/perl-5.32.0/"
  @INC:
    ./lib
    /Users/damian/perl5/perlbrew/perls/perl-5.32.0/lib/perl5/darwin-thread-multi-2level/
    /Users/damian/perl5/perlbrew/perls/perl-5.32.0/lib/perl5/darwin-2level/
    /Users/damian/perl5/perlbrew/perls/perl-5.32.0/lib/perl5/darwin-2level
    /Users/damian/perl5/perlbrew/perls/perl-5.32.0/lib/perl5
    /Users/damian/perl5/perlbrew/perls/perl-5.32.0/lib/5.32.0/darwin-2level
    /Users/damian/perl5/perlbrew/perls/perl-5.32.0/lib/5.32.0
    /Users/damian/perl5/perlbrew/perls/perl-5.32.0/lib
    /Users/damian/perl5/perlbrew/perls/perl-5.32.0/lib/site_perl/5.32.0/darwin-2level
    /Users/damian/perl5/perlbrew/perls/perl-5.32.0/lib/site_perl/5.32.0
    /Users/damian/perl5/perlbrew/perls/perl-5.32.0/lib/5.32.0/darwin-2level
    /Users/damian/perl5/perlbrew/perls/perl-5.32.0/lib/5.32.0