Hi Alex and Chris,
Love the show. It's exactly why I got in to Linux in the first place. I'm also having a great time listening about Project Off-grid as I am about to move to a rural place in Australia with no services (well, it's got a (dirt) road) and build something from the ground up.
I'm writing about your Degoogling Challenge as it is something I embarked upon a few years ago. I'm not fully out yet but I thought I would share some of the alternatives I've been using particularly on the Android phone front:
Google Maps -> OsmAnd [http://osmand.net/] This is great but ultimately relies on good maps data. The data can be downloaded locally to your device which is great for spotty reception and can include topo maps, Wikipedia entries of landmarks and similar. I've found some behavioral changes make it viable for me. When I am planning a trip somewhere I check how good the OpenStreetMap data is and might fill some in myself before I go then it will be there when I travel. Unfortunately there isn't a good replacement for the reviews that are tied to Google Maps.
Play Store -> Aurora Store. This is an alternative front end for Google Play which keeps your data away while giving you access to those apps that are exclusive. Looking at you Starlink. There is also Aurora for F-Droid and other FOSS repos.
Gmail -> Proton Mail. I pay for the Plus service and it's good for what I need. I'm hardly what you'd call a big email user though, I don't run a business through it or anything.
Google Docs, Calendar, Contacts, Tasks -> Nextcloud. Self-hosted of course with the OpenOffice plugin for Docs and DAVx5 for Calendar, Contacts and Tasks.
That's probably enough info dump for you right now. Good luck with the challenge and remember "If it's worth doing, it's worth doing badly." getting rid of some spying cloud services for a self hosted alternative is better than getting rid of none.
Hit me up for a visit if you're ever in Australia. Hopefully my own project off-grid will be ready for guests.
Regards,
Ross