Need a new copy of LR6 because old copy corrupted due to computer crash

You MIGHT (or might not) be able to get Lr 6 from The Internet Archive, see https://community.adobe.com/t5/lightroom-classic-discussions/p-lightroom-6-14-download-is-no-longer-available-on-adobe-servers/m-p/14357593#M352977

It is unlikely that you will be able to install and activate Lr 6. There was a report of success in the last month using a complicated procedure, but I cannot find the link, nor can I confirm it still works  here is a brief description of the procedure. In my opinion, the best solution is to upgrade to Lightroom Classic.