Yes, thanks! After finding several parser scripts/libraries on github for php, I realised they were all too complicated for my use case. In the end I wrote a small php script that goes through the ics file line by line and ran it locally. For each event found it created or appended a file for that date. This didn’t process repeating events, and only captured the start date of a multiday event but that is good enough for me. Now I have backfilled my Daylogs for the years 2007-2020 into Obsidian.
Update: 2024/09/22 upon request I shared the script I made at GitHub - tonzyl/parse_ics_to_md: small php script to turn events in an ICS file into markdown notes by date (CC0, public domain dedication)