Hello @bionewbie
The Galaxy wrapped version of Gemini works with the hg19 genome. There are technical reasons why hg38 is not supported.
Quote from the tool form, as hosted at https://usegalaxy.eu: Gemini load
Only build 37 (aka hg19) of the human genome is supported.
GTN Tutorial that covers an example usage: Exome sequencing data analysis for diagnosing a genetic disease
Gemini has unique functionality. Annotation and parsing tools are all one package. But there are many other tools to annotate/parse VCF datasets. Please see this prior Q&A for some tips: GEMINI load alternatives
Best!