extreme slow working after update

I have just updated my rp3 running dietpi using the method offered by dietpi: dietpi-update.
Then i have noticed the nextcloud became slow. I have run the ncc scan which reported the lower version of ncc then the one shown in ncc
21.0.4 shown in ncc vs 20.0.9 by the scan.
After searching i wanted to check my debian version but i am not sure how to do that.
So my question is how to check debian, dietpi and ncc version and if necessary how to update them manually

First try to perform a reboot and check your system afterwards how it is going.

DietPi can be checked using dietpi-update or by running cat /boot/dietpi/.version
Debian packages can be updated using apt update && apt upgrade
OS version can be display using cat /etc/os-release
For Nextcloud you could do following to perform a manual update if needed

ncc maintenance:mode --on
sudo -u www-data php7.3 /var/www/nextcloud/updater/updater.phar
ncc maintenance:mode --off

thank you, it works as you said. I will update debian to 11.

but still my question is:
why my system that was perfect until, became so ruggish and slow after update? how can i check possible reasons?

Can you share more details what part of Nextcloud has become slow? Is it browsing the web interface, or uploading/downloading files?

Also can you share the output of the following command:

cat /var/tmp/dietpi/logs/dietpi-update.log

So we can see which APT packages have been upgraded along with the DietPi update.