Thank you the responses
. It looks like both Electrum & Samourai do not require GSF. Great suggestions that I will try out.
Google related services and frameworks only apply to pre-installed apps
(installed apps that you will see upon opening a brand new phone for the first time), Google apps
(GAPPS) and to some number of apps
(not literally all apps in Google play). Like for example, most of the online games, it needs Google Play Services. The framework also covers most of the Android service components of the device.
Since your concern is about an app, you can test any app if they will work without the framework or Google Play Services. Just disable all the Google related services at the Settings > Apps
(vary per Phone but easy to locate) since you can't remove or uninstall it unrooted then just install your preferred app.
Once disabled, you won't be able to update any apps via Playstore obviously. You won't now have a preview of others app as well if a new and updated version has arrived. To solve this, you must be updated and you need an .apk file of the latest version to overwrite the previous one. Sounds hassle indeed.
Concern about privacy? Or worried that Google might collect data?