ok today i just flashed 21.04 Ubuntu desktop…on an m-2 240 gig chip…
apt update …etc usual  install ok to change from the hippo desktop to ubuntu mate…
apt purge ubuntu-desktop*
apt install ubuntu-mate desktop*
i use light DM as a display manager
when prompted it was the only question i got asked during the desktop upgrade…
after the code has finished type  reboot
open a terminal after the reboot and start as super user…
apt auto remove
reboot
reopen a terminal as root
i edited the  config.txt and set the  cpu stats…2200 seems to be their sweet spot…also up the top you can add a temp gauge simply by adding to the top panel click and open a command prompt from the  menu in the add to panel…
in the text box type
cat  /sys/class/thermal/thermal_zone0/temp
close that and you should see the  temp of the cpu up the top…
arm_freq=2200
over_voltage=8
gpu=*
set to 500 or leave blank omit  that is i men set it to 500 on mine…not running any case just an argon 40 fan and a heat sink flat black ribbed 40x20
up the top panel open the cpu frequency monitor its basically the governor control
it will be set to default but you have to set it after every reboot or start up …my kernel  rebuild is limited…but you can  re-flash the kernel if you know how and set it to what you require…
reboot  enjoy…
footnote i set in the  software updater for source code and the conical  options in their also…dont touch  um…
additional dev updates unless your prepared to  expect  it will most likely case crashes and discomfort to your usb ports…etc…etc…
lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 21.04
Release:	21.04
Codename:	hirsute
uname -a
Linux mach-desktop 5.11.0-1007-raspi #7-Ubuntu SMP PREEMPT Wed Apr 14 22:08:05 UTC 2021 aarch64 aarch64 aarch64 GNU/Linux
neofetch report…
  -+ssssssssssssssssssyyssss+-         OS: Ubuntu 21.04 aarch64 
.ossssssssssssssssssdMMMNysssso.       Host: Raspberry Pi 4 Model B Rev 1.2 
/ssssssssssshdmmNNmmyNMMMMhssssss/      Kernel: 5.11.0-1007-raspi
+ssssssssshmydMMMMMMMNddddyssssssss+     Uptime: 55 mins
/sssssssshNMMMyhhyyyyhmNMMMNhssssssss/    Packages: 2135 (dpkg), 6 (snap)
.ssssssssdMMMNhsssssssssshNMMMdssssssss.   Shell: bash 5.1.4
+sssshhhyNMMNyssssssssssssyNMMMysssssss+   Resolution: 1920x1080
ossyNMMMNyMMhsssssssssssssshmmmhssssssso   WM: Metacity (Marco)
ossyNMMMNyMMhsssssssssssssshmmmhssssssso   Theme: Adwaita [GTK3]
+sssshhhyNMMNyssssssssssssyNMMMysssssss+   Icons: Adwaita [GTK3]
.ssssssssdMMMNhsssssssssshNMMMdssssssss.   Terminal: mate-terminal
/sssssssshNMMMyhhyyyyhdNMMMNhssssssss/    CPU: BCM2835 (4) @ 2.200GHz
+sssssssssdmydMMMMMMMMddddyssssssss+     Memory: 1808MiB / 3738Mi
enjoy…