Looks like fixing bug#45341 introduced a regression WRT bug#44568: font 
lock of assignments with type hints

Load the code below or see  "var3: Mapping" in center of attached png

---

# from typing import Mapping, Tuple, Sequence
var1: int = 5
var2: Mapping[int, int] = {10: 1024}
var3: Mapping[Tuple[int, int], int] = {(2, 5): 32}
var4: Sequence[Sequence[int]] = [[1], [1, 2], [1, 2, 3]]
var5: Sequence[Mapping[str, Sequence[str]]] = [
     {
     'red': ['scarlet', 'vermilion', 'ruby'],
     'green': ['emerald', 'aqua']
     },
     {
     'sword': ['cutlass', 'rapier']
     }
]

[a, b, c] = 1, 2, 3
a, *b, c = range(10)
inst.a, inst.b, inst.c = 'foo', 'bar', 'baz'
(a, b, *c, d) = x, *y = 5, 6, 7, 8, 9

---


In GNU Emacs 28.0.50 (build 1, i686-pc-linux-gnu, GTK+ Version 3.14.5, 
cairo version 1.14.0)
  of 2020-12-27
Repository revision: df882c9701755e2ae063f05d3381de14ae09951e
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.11604000
System Description: Debian GNU/Linux 8 (jessie)

Configured using:
  'configure --with-mailutils -with-modules --with-ffi'

Configured features:
XPM JPEG TIFF GIF PNG CAIRO SOUND DBUS GSETTINGS GLIB NOTIFY INOTIFY ACL
GNUTLS LIBXML2 FREETYPE LIBOTF ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 XDBE
XIM MODULES THREADS PDUMPER

Important settings:
   value of $LANG: de_DE.UTF-8
   locale-coding-system: utf-8-unix

Major mode: Python

Minor modes in effect:
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   tooltip-mode: t
   global-eldoc-mode: t
   eldoc-mode: t
   electric-indent-mode: t
   mouse-wheel-mode: t
   tool-bar-mode: t
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Load-path shadows:
None found.

Features:
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epg-config gnus-util rmail rmail-loaddefs text-property-search mm-decode
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seq byte-opt gv bytecomp byte-compile cconv comint ring cl-loaddefs
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vc-hooks lisp-float-type mwheel term/x-win x-win term/common-win x-dnd
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backquote threads dbusbind inotify dynamic-setting system-font-setting
font-render-setting cairo move-toolbar gtk x-toolkit x multi-tty
make-network-process emacs)

Memory information:
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