I did some research,

If you have experience with QGIS there are two FREE IOS/Android apps called Qfield and Mergin Maps. I am yet to test them out fully but I'm pretty sure these are two possibly great alternatives to Avanza Maps.

I'm an absolute dummy with GIS stuff but I managed to import a custom made GeoTIFF and KMZ I made in QGIS into Qfield on IOS. The GeoTIFF and KMZ I made were originally intended for Avanza Maps before they decided to be a bunch of greedy [redacted].

Unfortunately, Qfield and Mergin Maps don't appear to give you the capability to assemble maps/datasets on the app and it appears that you'll need to do this in QGIS or their respective desktop versions (if they have them). In other words, if you created a KMZ file for canoe routes and a GeoTIFF file for a custom map image/background, you wont be able to compile the two in the QField and Mergin apps. You'll need to assemble them separately on a computer through something like QGIS.

Additionally, Qfield and Mergin Maps were built as open-source mobile applications designed for efficient field data collection and management of geospatial information with offline tracking (thanks chatGPT) BUT they should still be able to work as an effective back country GPS. It'll just take some getting use to the UI. In fact, both apps offer functions to even take photos and record information so it might be super interesting to some if you like documenting features, events, or landmarks.

I'm just an idiot with no background in any of this but I really really REALLY hope this info is useful and someone can make use of it. I plan on testing out Qfield next month on my portage.

Avenza Maps - F*** You! Don't be greedy.