To reproduce, customize pop-up-frames to non-nil and set up your window
manager such that it doesn't automatically set input focus on newly
created frames.

Now in an xref-mode buffer, press RET on a search result
(xref-goto-xref) and notice that the newly created frame doesn't receive
input focus. That is because xref-goto-xref uses `display-buffer',
followed by a `select-window'.

To contrast this behaviour with grep-mode, pressing RET in a grep-mode
buffer (compile-goto-error) does set input focus to the newly created
frame. That is because compile-goto-error uses `pop-to-buffer`, which
also calls `select-frame-set-input-focus'.

Best regards.

In GNU Emacs 29.0.50 (build 4, x86_64-pc-linux-gnu, GTK+ Version 3.24.33, cairo version 1.17.6)
 of 2022-06-14 built on miha-pc
Repository revision: 175bc8e5a53740432c844b5aae1981d4f47c96f7
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101003
System Description: Arch Linux

Configured using:
 'configure --prefix=/usr --without-libsystemd'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBXML2 M17N_FLT MODULES NOTIFY INOTIFY PDUMPER PNG
RSVG SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS WEBP X11
XDBE XIM XINPUT2 XPM GTK3 ZLIB

Important settings:
  value of $LANG: en_US.utf8
  locale-coding-system: utf-8-unix

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  blink-cursor-mode: t
  buffer-read-only: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media rmc puny
dired dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg
rfc6068 epg-config gnus-util text-property-search time-date seq gv
subr-x byte-opt bytecomp byte-compile cconv mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs
cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
iso-transl tooltip eldoc paren electric uniquify ediff-hook vc-hooks
lisp-float-type elisp-mode mwheel term/x-win x-win term/common-win x-dnd
tool-bar dnd fontset image regexp-opt fringe tabulated-list replace
newcomment text-mode lisp-mode prog-mode register page tab-bar menu-bar
rfn-eshadow isearch easymenu timer select scroll-bar mouse jit-lock
font-lock syntax font-core term/tty-colors frame minibuffer nadvice
simple cl-generic indonesian philippine cham georgian utf-8-lang
misc-lang vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms
cp51932 hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese composite emoji-zwj charscript charprop case-table
epa-hook jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button
loaddefs faces cus-face macroexp files window text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit xinput2 x multi-tty make-network-process
emacs)

Memory information:
((conses 16 44772 6206)
 (symbols 48 5717 0)
 (strings 32 15673 1842)
 (string-bytes 1 515461)
 (vectors 16 11098)
 (vector-slots 8 161431 8182)
 (floats 8 20 54)
 (intervals 56 340 1)
 (buffers 992 11))