Joomla/PHP Expert for PHP + backend upgrade

We run a website for a boutique financial services firm. The site is built on Joomla and the current design works well for us, so no redesign or front-end changes are required. The website is hosted with one.com.

However, the backend is overdue for maintenance and upgrades. The site is currently running:
• Joomla 3.10.11
• PHP 8.0
• MariaDB 10.6.23

We need a Joomla/PHP expert to safely update the site so it runs on the latest stable Joomla version and a current supported PHP version.

Scope of work:
• Create a separate staging environment for the website.
• Upgrade to the latest stable version.
• Update all plugins/extensions and ensure compatibility.
• Upgrade PHP to the latest stable version supported by Joomla.
• Fully test the site on staging to ensure nothing breaks.
• Deploy updates to the live site.

Important:
• The current design and layout must remain unchanged.
• Should have strong Joomla and PHP experience.

Please include:
• Examples of previous Joomla upgrade work.
• Estimated timeframe (we're aiming for completion within the next 2 weeks).