Slipping Audio in Source Settings is not Perf Slip and I don’t think it translates to Pro Tools etc.
Traditional import should still append metadata, but if the recorder in questions doesn’t write this basic data into the Bext section of the WAV metadata, it will likely not be seen by traditional import. The iXML section of the medata is not seen by traditional import, and it is seen by AMA, AFAIK.
But I don’t think there should be a difference between 2018.x and 2020.x in any of this.
You mention being on 2020.10, have you been able to try it on 2020.12?
Oh, one more thing, on 2020.10, under the Audio Import settings, I see a tick box that says “Use Broadcast Wave Scene and Take for Clip Names”. Seems that it a setting you should double check. If that setting does not show, you are likely using older user settings on a newer version of MC. Rebuild your settings (or at the very least create fresh Import settings).