APCu is a data cache, and it is available in most Linux distributions. On Red Hat/CentOS/Fedora systems install php-pecl-apcu. On Debian/Ubuntu/Mint systems install php-apcu.

$ sudo apt install php-apcu
[sudo] password for user:
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following additional packages will be installed:
  php8.1-apcu
The following NEW packages will be installed:
  php-apcu php8.1-apcu
0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
Need to get 48.9 kB of archives.
After this operation, 197 kB of additional disk space will be used.
Do you want to continue? [Y/n] Y

sudo apt install php-apcu
[sudo] password for user:

Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following additional packages will be installed:
  php8.1-apcu
The following NEW packages will be installed:
  php-apcu php8.1-apcu
0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
Need to get 48.9 kB of archives.

Selecting previously unselected package php8.1-apcu.e will be used.
(Reading database ... 83934 files and directories currently installed.)
Preparing to unpack .../php8.1-apcu_5.1.21+4.0.11-7ubuntu1_amd64.deb ...
Unpacking php8.1-apcu (5.1.21+4.0.11-7ubuntu1) ...
Selecting previously unselected package php-apcu.
Preparing to unpack .../php-apcu_5.1.21+4.0.11-7ubuntu1_amd64.deb ...
Unpacking php-apcu (5.1.21+4.0.11-7ubuntu1) ...
Setting up php8.1-apcu (5.1.21+4.0.11-7ubuntu1) ...
Setting up php-apcu (5.1.21+4.0.11-7ubuntu1) ...
Processing triggers for libapache2-mod-php8.1 (8.1.2-1ubuntu2.11) ...
Processing triggers for php8.1-cli (8.1.2-1ubuntu2.11) ...
Scanning processes...
Scanning processor microcode...
Scanning linux images...
Get:1 http://us.archive.ubuntu.com/ubuntu jammy/universe amd64 php8.1-apcu amd64 5.1.21+4.0.11-7ubuntu1 [45.7 kB]
Running kernel seems to be up-to-date.ntu jammy/universe amd64 php-apcu amd64 5.1.21+4.0.11-7ubuntu1 [3,132 B]
Fetched 48.9 kB in 0s (105 kB/s)
The processor microcode seems to be up-to-date.

No services need to be restarted.

No containers need to be restarted.

No user sessions are running outdated binaries.

No VM guests are running outdated hypervisor (qemu) binaries on this host.

Now, restart apache2 webserver

sudo systemctl restart apache2

After restarting your Web server, add this line to your NextCloud's config.php file:

'memcache.local' => '\OC\Memcache\APCu',

Where to find your config.php file:

cd /var/www/[path to nextcloud installation]/nextcloud/config/

ls -l

Which lists the config.php file

sudo vim config.php

Edit the file with vim editor to insert the following line:

'memcache.local' => '\OC\Memcache\APCu',