KeepassXC is great, but I realised very late in the process of setting it up, that the browser extension does not support Flatpak based browsers: “Please note that in general Flatpak and Snap based browsers are not supported, Ubuntu’s Firefox Snap being an exception.” (https://github.com/keepassxreboot/keepassxc-browser/wiki/Troubleshooting-guide)
I hope this might change at some point.
LineageOS has instructions for Windows/Mac/Linux: https://wiki.lineageos.org/adb_fastboot_guide