"Ultimo theme and the developer has abandoned updating after Magento 2.3.1"

Does anyone know if this is true as I am currently using Ultimo and plan to use it in future Magento releases.

It appears so. It seems to work through Magento 2.3.6, but it absolutely breaks in 2.4. It’s very disappointing that Envato is still advertising an abandonware product without any warnings or alerts.