At JPG 90% it looks the same. Keep the HEIC as the original for editing.

Do date and location survive?

The date does. To drop the location (GPS), run the JPG through "Remove metadata".

Open iPhone HEIC photos on Windows

A HEIC someone sent will not open. As a JPG it opens anywhere.

Drop the photos on "HEIC to JPG". One at a time is free; batches with the Pass.
Quality 90% is plenty. Save, and it is a JPG.
For the future, set the iPhone camera to "Most Compatible" to shoot JPG from the start.

Does quality suffer?: At JPG 90% it looks the same. Keep the HEIC as the original for editing.
Do date and location survive?: The date does. To drop the location (GPS), run the JPG through "Remove metadata".

Pictures are never sent anywhere; everything runs in this browser.