Software jobs for sure, but I've been applying for jobs with employers that have other types of jobs too (nursing, accounting, industrial engineering, etc.) and the requirement is not solely for their software jobs. Some have fields that pattern match (for these I put something like "https://linkedin.com/I_DO_NOT_USE_LINKEDIN") while others use an integration that actually require you to sign in to Linkedin (some of these I've created accounts for and then deleted them, some I've managed to bypass by hacking on the POST a bit, and others I've decided not to apply for).

I got an email from Indeed for this today: https://job-boards.greenhouse.io/doordashusa/jobs/7727512

About 2/3 of the way down you can see LinkedIn Profile, and it's a mandatory field.

There are tons though.