Laravel Server Requirements mentions that BCMath, Ctype, JSON, Mbstring, OpenSSL, PDO, Tokenizer and XML extensions are required. Most the extensions are installed and enabled by default.
You can run the following command in Ubuntu to make sure the extensions are installed.
sudo apt install openssl php-common php-curl php-json php-mbstring php-mysql php-xml php-zip
PHP version specific installation (if PHP 7.4 installed)
sudo apt install php7.4-common php7.4-bcmath openssl php7.4-json php7.4-mbstring
You may need other PHP extensions for your composer packages. Find from links below.
PHP extensions for Ubuntu 16.04 LTS (Xenial)
PHP extensions for Ubuntu 18.04 LTS (Bionic)
Hope This works!!