From Ian Grieve comes info that Microsoft Dynamics GP 2018 R2 Displays Full Screen By Default. This was an issue with certain monitors that would make come items display very small without a good option to fix it.
— Read on www.azurecurve.co.uk/2019/08/microsoft-dynamics-gp-2018-r2-displays-full-screen-by-default/
Microsoft Dynamics GP 2018 R2 Displays Full Screen By Default – azurecurve
Microsoft & the GP EcosystemGP 2018
Archived post from 2019. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.