Migrate from Lightroom to Photos

If you hold down the Option key while dragging the thumbnail to the Desktop you'll get the original file, RAW or jpeg.

You're travelling from a much more powerful professional grade application to a weaker, give-away consumer one. There is no easy way to do it. There are mp plug-in etc, to help, as frankly, the traffic is usually the other way. Your best bet is to work in batches - say, year by year - exporting from Lightroom and then importing to Photos, recreating your structure as you go.

Also, be sure you export a batch and use it as a test run. See how metadata is handled and so on. Take the time to explore the options available to you in Photos. You may not edit much anymore, as you say, it Photos is also a much more limited photo manager. Photos is a give-away, and you get what you pay for.

That means that you export, writing your metadata to the files, from Lightroom to the Finder, in what ever format you choose - original raws and/or edited Jpegs or tiffs. Assuming that the camera you use/used is supported then Photos will have no problem importing the Raws. And these Raws will be perfectly possible to retrieve again using there Export command in Photos (file -> Export -> Unmodified Original). There is some confusion here as some folks assume that drag and drop or sharing to another app will, in fact, yield the Raw. It doesn't. It yields a Jpeg preview. Only using the Export command can you access the Raw.

Thanks for that clarification. Good to know.