You can use Imaris File Converter to convert your czi file into Imaris format in the background without using Imaris license (the new version has different icon)
Imaris 8.4.x identify the memory size of the graphic card correctly.
If you use older version Make sure that File=>Preferences=>Display Texture cache limit is set to the size of the memory on the graphics card (12000 MB on 30T/80T, 24000 MB on 80T)
You can use Imaris File Converter to convert your czi file into Imaris format in the background without using Imaris license (the new version has different icon)Before the first use of Imaris File converter make sure to increased the "Memory Limit" to 150000 MB by clicking the "Preferences..." button and setting the proper value