Drupal 7 is currently moved into the legacy mode and will reach End Of Life by end of next year. If you are still using Drupal 7, here are some challenges you will soon encounter.
No new features
As there are not many development activities happening around Drupal 7. You cannot expect any new features to come in Drupal 7 core. For contributed modules also things are not different. Maintainers are not focusing on Drupal 7 versions and whatever maintenance activities happening will be minimal.
Security
Even though Drupal 7 core will be maintained till it reaches the end of life, the module maintainers may not follow that. It is an additional effort to keep the software updated for multiple versions. There is a chance that more contributed modules remove their support for Drupal 7 and if you are using those modules you will be in trouble.
Coping up with PHP versions
New versions of PHP and other libraries are released regularly. Currently, the latest version of PHP is 8.1 The latest version of Drupal 7 does not support PHP 8.1 yet. There are many contributed modules that also do not support the latest PHP versions. This will create issues with hosting - where hosting providers upgrade their infrastructure. This will also affect the chance of using the improved performance available with the latest version of PHP.