Hi-DPI scaling broken on 2-in-1 Dell XPS 13 notebook

 * Cinnamon version 4.6.6 
 * Distribution - (Mint 20 Ulyana)
 * Intel HD Graphics 615 vendor: Dell driver: i915
 * 64 bit

Issue

On Dell XPS 13 2-in-1 notebook, Hi-DPI scaling is randomly broken (i.e. icons and text are very small) immediately after logging in; it is systematically broken if the notebook is rotated and the screen changes to vertical configuration.

Steps to reproduce

First way:

1. Keep "Cinnamon Settings Daemon - xrandr" activated with no delay
2. log in and out - approximately half of the times the DPI scaling is ignored and text and icons are very small.
   The bad behavior disappears if the "Cinnamon Settings Daemon - xrandr" is disabled;
   The bad behavior is highly mitigated if the "Cinnamon Settings Daemon - xrandr" starts 10s after login;

Second way:

1. With "Cinnamon Settings Daemon - xrandr" activated, rotate the notebook to cause screen reconfiguration to vertical mode: DPI scaling settings are ignored.
2. With "Cinnamon Settings Daemon - xrandr" activated, rotate the notebook to cause screen reconfiguration to horizontal mode: DPI scaling settings are ignored.

Expected behaviour

I would expect that DPI scaling is applied irrespective of the screen orientation. My impression is that DPI scaling is applied only at logon and in the monitor resolution dialog, and is ignored in any other automatic reconfiguration event.

Other information

Configuration info, if applicable
If this bug report is related to an Applet, Desklet or Extension, please paste (or use a pastebin service) the offending extension's settings, if it has any. You can obtain this by opening its configuration, clicking the 'hamburger' button in the upper-right corner of the window, and selecting "Export to a file". Please be sure to review the contents and remove any personal data it may contain.

System:
  Kernel: 5.4.0-40-generic x86_64 bits: 64 compiler: gcc v: 9.3.0 
  Desktop: Cinnamon 4.6.6 wm: muffin dm: LightDM 
  Distro: Linux Mint 20 Ulyana base: Ubuntu 20.04 focal 
Machine:
  Type: Convertible System: Dell product: XPS 13 9365 v: N/A 
  serial: <filter> Chassis: type: 31 serial: <filter> 
  Mobo: Dell model: 0KP45X v: A00 serial: <filter> UEFI: Dell v: 1.0.21 
  date: 08/08/2017 
Battery:
  ID-1: BAT0 charge: 44.3 Wh condition: 45.2/46.0 Wh (98%) volts: 8.7/7.6 
  model: LGC-LGC6.130 DELL NP0V377 serial: <filter> status: Discharging 
CPU:
  Topology: Dual Core model: Intel Core i7-7Y75 bits: 64 type: MT MCP 
  arch: Amber Lake rev: 9 L2 cache: 4096 KiB 
  flags: avx avx2 lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx 
  bogomips: 12799 
  Speed: 600 MHz min/max: 400/3600 MHz Core speeds (MHz): 1: 600 2: 600 
  3: 600 4: 600 
Graphics:
  Device-1: Intel HD Graphics 615 vendor: Dell driver: i915 v: kernel 
  bus ID: 00:02.0 chip ID: 8086:591e 
  Display: x11 server: X.Org 1.20.8 driver: modesetting unloaded: fbdev,vesa 
  resolution: 3200x1800~60Hz 
  OpenGL: renderer: Mesa Intel HD Graphics 615 (KBL GT2) v: 4.6 Mesa 20.0.8 
  direct render: Yes 
Audio:
  Device-1: Intel Sunrise Point-LP HD Audio vendor: Dell 
  driver: snd_hda_intel v: kernel bus ID: 00:1f.3 chip ID: 8086:9d71 
  Sound Server: ALSA v: k5.4.0-40-generic 
Network:
  Device-1: Intel Wireless 8265 / 8275 driver: iwlwifi v: kernel port: efa0 
  bus ID: 3c:00.0 chip ID: 8086:24fd 
  IF: wlp60s0 state: up mac: <filter> 
  IF-ID-1: docker0 state: down mac: <filter> 
Drives:
  Local Storage: total: 476.94 GiB used: 181.42 GiB (38.0%) 
  ID-1: /dev/nvme0n1 vendor: Toshiba model: KXG50ZNV512G NVMe 512GB 
  size: 476.94 GiB speed: 31.6 Gb/s lanes: 4 serial: <filter> 
Partition:
  ID-1: / size: 241.18 GiB used: 181.35 GiB (75.2%) fs: ext4 
  dev: /dev/nvme0n1p7 
  ID-2: swap-1 size: 7.87 GiB used: 0 KiB (0.0%) fs: swap 
  dev: /dev/nvme0n1p8 
Sensors:
  System Temperatures: cpu: 39.5 C mobo: 29.8 C 
  Fan Speeds (RPM): N/A 
Repos:
  No active apt repos in: /etc/apt/sources.list 
  Active apt repos in: /etc/apt/sources.list.d/mono-official-vs.list 
  1: deb https://download.mono-project.com/repo/ubuntu vs-bionic main
  Active apt repos in: /etc/apt/sources.list.d/official-package-repositories.list 
  1: deb http://packages.linuxmint.com ulyana main upstream import backport #id:linuxmint_main
  2: deb http://archive.ubuntu.com/ubuntu focal main restricted universe multiverse
  3: deb http://archive.ubuntu.com/ubuntu focal-updates main restricted universe multiverse
  4: deb http://archive.ubuntu.com/ubuntu focal-backports main restricted universe multiverse
  5: deb http://security.ubuntu.com/ubuntu/ focal-security main restricted universe multiverse
  6: deb http://archive.canonical.com/ubuntu/ focal partner
Info:
  Processes: 230 Uptime: 6m Memory: 7.64 GiB used: 2.03 GiB (26.6%) 
  Init: systemd v: 245 runlevel: 5 Compilers: gcc: 9.3.0 alt: 7/9 
  Shell: bash v: 5.0.17 running in: gnome-terminal inxi: 3.0.38 

Start by reproducing the issue with Cinnamon Settings Daemon - xrandr enabled, both after login and while rotating the Dell XPS 13. Trace how automatic display reconfiguration handles the current orientation and DPI scaling, comparing it with the monitor resolution dialog behavior described here. Done means scaling remains applied after login and every tested orientation change.