Hi,
XlsxAdapter is from FlexCel 3, and indeed, flexcelvclreg.zip (the FlexCel 3 file) was removed from the download page. We removed it because too many customers were getting confused and downloading FlexCel 3 instead of 7 because they misclicked the link.
But FlexCel 3 is still available and adapted for Delphi 11 too. Just mail to info@tmssoftware.com with your registration data, and they will send you the latest FlexCel 3.