Using GSA 8.0 (beta2) and I am unable to have reports downloaded in HTML Format.
I tried to upload from file exported from GSA 7.0.2 but I am being displayed an empty dialog box with error headlined.
I tried to download plugins from https://www.greenbone.net/technology/report_formats.html but its 404.
So this is not the Community Edition (GCE) which this category is about but the Source Edition (GSE). Moving to the correct category accordingly.
Please also note that GSA 8.0 (beta2) is a quite outdated release. Try to update to the latest stable releases listed in GVM-10 (stable, initial release 2019-04-05) and check if your issue is solved there.
In GSE gvm-10 support for HTML report export was removed: