Migrating Full Sites
After migrating an Oxygen site or changing the domain in your hosting, you must follow these steps in order:
Run a search and replace on the database to update the old domain to the new domain (the Better Search Replace plugin is good for this). This isn't needed if you have used a migration plugin that runs a search and replace for you, such as All In One Migration
Save your permalinks twice via Settings > Permalinks
Resign your shortcodes via Oxygen > Settings > Security
Regenerate your CSS cache via Oxygen > Settings > CSS Cache
Re-save your licence key via Oxygen > Settings > License so that your site can use one-click updates when a new version is available
You may also need to open each template in the admin area and click the Update button on the right-hand side but I've only found that to be required on a handful of sites.
If you have any caching plugins installed you will also need to clear the caches.
Migrating Individual Pages or Templates
Manually Copy & Pasting
If you've not used any classes/selectors in your design, you can copy your page/template shortcodes to another site by clicking +Shortcodes below the "Edit with Oxygen" button, copying those shortcodes and pasting them into the same location on a new site.
If you have used classes/selectors, then you would need to copy Oxygen's Export JSON first, as that contains all your Global settings, Classes, Selectors & Stylesheets. You can find it via Oxygen > Export & Import.
Utilising Oxygen's User Design Library
It's possible to make your site a design set that can then be accessed by other sites. There's more information on this here: https://oxygenbuilder.com/documentation/design-library/user-design-library/.
Using a Plugin
The paid, third-party plugin, Hydrogen Pack allows you to copy and paste designs between sites: https://www.cleanplugins.com/products/hydrogen-pack/.