You need a USB-C (male) to USB A (female) adaptor, which may be described as "OTG" (ie. same thing you'd use to connect a USB flash drive to your phone). If you plug the eTrex in and wait an implausibly long time, the eTrex and its SD card should eventually mount, and you'll be able to copy files back and forward using your file manager of choice.
Uploading to Strava is a tricky one, because the Strava app has no concept of "upload this file". The website works fine, though (possibly in desktop mode - it's been a while since I've done it, my preferred workflow is to SCP the file to my server as a backup, where I have a small shell script to handle the upload to Strava).
You can open the track locally in apps like OSMAnd or Viewranger, and even create Routes to copy to the eTrex.