Build permanently shut down on Feb 1st, 2024

Hi @J.AWC, when you get a chance, please introduce yourself here. I'd also encourage you to add a real picture as your avatar because it helps build community!

The .xml forms that were built in Build will continue to work just as normal because they don't live in Build. They live in whatever server (e.g., Aggregate, Central) you uploaded or published them to. And they will continue to work on that server and with any client (e.g., Collect) connected to that server.

Despite this, you should export all your Build forms to XLSForm out of an abundance of caution. It ensures you have a backup copy of the forms you designed in a format that is easy to edit.

XLSForm is free to use, but it's a form design format/document so comparing it to Build/Collect isn't appropriate because those are tools/apps/systems that build/process/render those forms.

I get the sense you want to know the recommend end-to-end path for users to follow. We detail that at https://docs.getodk.org/getting-started, but to summarize, we recommend you design forms with XLSForm, upload the forms to Central server (self-hosted or running in ODK Cloud), and fill out the forms with the Collect mobile app and send them to Central, and download the form data back from Central UI.

All the above software above is open-source and available at no cost. ODK Cloud, is a paid service, but you aren't paying for the software, you're paying for fully-managed and supported hosting of Central.