Unicode fonts not correctly displayed

[Toni Schmidbauer <toni+help-gnu-emacs@stderr.at>]

hi,

i'm currently struggling with my font config in emacs:

========
(when (member "JetBrainsMono Nerd Font" (font-family-list))
  (set-face-attribute 'default nil :font "JetBrainsMonoNerdFont")
  (set-frame-font 'default "JetBrainsMonoNerdFont 20")
  (set-face-font 'default "JetBrainsMonoNerdFont 20")
  (set-face-font 'variable-pitch "JetBrainsMonoNerdFont 20"))

;; Emoji: 😄, 🤦, 🏴󠁧󠁢󠁳󠁣󠁴󠁿
(set-fontset-font t 'symbol "Segoe UI Emoji" nil 'append)
(set-fontset-font t 'symbol "Segoe UI Symbol" nil 'append)
(set-fontset-font t 'symbol "Noto Color Emoji" nil 'append)

;; should include 2b22
(set-fontset-font t 'symbol "Symbola" nil 'append)

;; added just for testing, does not work
(set-fontset-font t ?⬢ "Symbola")
========

this is the minimal config i tried (commented out everything else in
init.el).

emoji's are rendered ok but the unicode glyph u002b22, which should be
part of the Symbola font does not render (emacs displays 2b22).

when i run what-cursor-position with a prefix arg i get the following
information:

========
             position: 874 of 1186 (74%), restriction: <40-1187>, column: 21
            character: ⬢ (displayed as ⬢) (codepoint 11042, #o25442, #x2b22)
              charset: unicode (Unicode (ISO10646))
code point in charset: 0x2B22
               script: symbol
               syntax: _ 	which means: symbol
             category: .:Base
             to input: type "C-x 8 RET 2b22" or "C-x 8 RET BLACK HEXAGON"
          buffer code: #xE2 #xAC #xA2
            file code: #xE2 #xAC #xA2 (encoded by coding system utf-8-unix)
              display: no font available

Character code properties: customize what to show
  name: BLACK HEXAGON
  general-category: So (Symbol, Other)
  decomposition: (11042) ('⬢')

There is an overlay here:
 From 853 to 887
  face                 hl-line
  priority             -50
  window               #<window 97 on *mu4e-draft*>


There are text properties here:
  fontified            t
========

so it tells me "no font available". i'm really struggling to understand
why...

any hints how this could be solved or debugged?

thanks for your valuable time

toni