Since you added the PHP-tag here is a online PHP testsite:
Link to the site
But i would recommend to you to hire a VPS where you can install everything you want and use SSH to log into.
Not entirely for your case but you can use VS Code Online as "full" fledged IDE in the webbrowser. You can work on local code when you don't have the rights to ...
Syncthing (syncthing.net) might meet your needs. Runs on Windows, but also on Linux & Mac. Open-source, encrypted file transfers, real-time syncing, optional file versioning. You should be able to install it on a cloud server and have it just sync to whatever you want on your local machine. No static ip requirement - it figures out routing by itself. ...
Visual Studio Code is a free open source IDE available on Windows, macOS and Linux (since you didn't mention your OS). Just add a PHP extension for the syntax. MySQL extensions are also available if you want. Otherwise, you also have Visual Studio Community, which is free.
For backing up data from servers, I'm using AzCopy v10 to synchronize local files to Azure Blob Storage.
Local copy can be considered always authoritative.
Only new/changed files are
Locally deleted files can be deleted from remote.
Azure Blob Storage has settings to automatically retain deleted blobs for some time period.
Azure offers additional ...