I can't help on the open source side but I find Komoot to be more user friendly and open. For example you can download GPX files without a subscription to then make trail bookmarks in open source apps like CoMaps.

This is great, thanks

CoMaps updates their map data weekly now. You need to click check for updates on the download maps page.

I use CoMaps for this. It took a little bit of time for me to get used to it but I now find it so much better than Google Maps bookmarks and I have moved everything over. CoMaps allows a wider range of pin colors and you can add detailed descriptions with each bookmark. No automatic cloud backup but I just export a backup to Proton Drive every couple of weeks or so, takes less than a minute to do so.

A useful app for this task is Geo Share. Helps opening links from Google Maps in other open source map apps.

Good luck finding your solutions!