Hello there, Nick. Yes, you can move your data from QuickBooks Desktop (QBDT) to QuickBooks Online (QBO). Since you can’t reinstall QBDT, you can install the 30-day trial version of QuickBooks Desktop 2021 to upgrade your backup file before transitioning to QBO. Please ensure your system meets the requirements for this version. (While this link is for the US version, the same principles apply to UK users.)
Once your backup is updated, you can use Movemybooks, a tool designed to convert and transfer your QBDT data directly into QBO. This tool ensures that your business data is migrated accurately while remaining MTD-compliant.
To help you understand the differences between QuickBooks Desktop and Online, you can check out this article: Moving from QuickBooks Desktop to Online? A feature comparison.
Feel free to revisit this thread if you have further questions or need clarification.