Lightroom 5 and New Computer

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Several years ago I purchased Lightroom 5 that has been installed on my laptop.  To maximize my editing I recently had built a desktop with the hope of having Lightroom 5 on the new build.  Now I'm struggling to do so even though I have the license number.  Thanks for any direction.  

[Rob_Cullen]

You may not be able to install v5.7 in new Operating Systems.

Mac Catalina or Big Sur -you positively cannot install!

PC Windows -10 install may be possible.

So what system do you have?

What obstacles are you encountering?

Any Error messages?