cat suits a twenty-line virtual host, not a 400 MB access log. Use less for anything large: Space and b page, /pattern searches and n repeats, g and G jump to the start and end, q quits. less -S stops long lines wrapping, and F follows a growing file like tail -f, with Ctrl-C returning you to scrolling. The same keys work in man and journalctl.
head and tail show the ends of a file; tail -f on the error log while you reload the page is the standard debugging move. Ubuntu 225 's logrotate 1,548 compresses Apache 129 logs from error.log.2.gz on; read those with zcat, zless and zgrep. /var/log/apache2 belongs to root and group adm, so you need sudo or membership of adm.
ls /var/log/apache2/ # root:adm, mode 750: not for you
sudo wc -l /var/log/apache2/error.log # how big is the problem?
sudo tail -n 2 /var/log/apache2/error.log | grep -o 'AH[0-9]*: .*' # newest two
zcat /usr/share/doc/apache2/changelog.Debian.gz | head -n 1 # read a .gz in placeOutput
ls: cannot open directory '/var/log/apache2/': Permission denied 17 /var/log/apache2/error.log AH00163: Apache/2.4.66 (Ubuntu) configured -- resuming normal operations AH00094: Command line: '/usr/sbin/apache2 -D FOREGROUND' apache2 (2.4.66-2ubuntu2.4) resolute-security; urgency=medium