> The other versions are native. It's one of the things that sets 1Password apart. Is the Linux version Electron?
Yes, it is very obvious from the screenshot that it’s built on top of Electron [1].
GTK nor Qt have that type of UI elements, they are obviously HTML elements stylized with CSS.
Another hint is in the files contained inside the Debian package used during the Linux installation [2]:
root@3cb1637b3070:/# apt-get download 1password
root@3cb1637b3070:/# dpkg --extract 1password_0.8.0-22506_amd64.deb temp
root@3cb1637b3070:/# ls -lia ./temp/opt/1Password/
total 177900
661008 drwxr-xr-x 5 root root 4096 Aug 3 18:23 .
661007 drwxr-xr-x 3 root root 4096 Aug 3 18:23 ..
661011 -rwxr-xr-x 1 root root 129796744 Aug 3 18:21 1password
661010 -rw-r--r-- 1 root root 1060 Aug 3 18:21 LICENSE.electron.txt
661023 -rw-r--r-- 1 root root 4710103 Aug 3 18:21 LICENSES.chromium.html
661021 -rwxr-xr-x 1 root root 6322128 Aug 3 18:21 chrome-sandbox
661017 -rw-r--r-- 1 root root 179981 Aug 3 18:21 chrome_100_percent.pak
661013 -rw-r--r-- 1 root root 321151 Aug 3 18:21 chrome_200_percent.pak
661022 -rw-r--r-- 1 root root 10505952 Aug 3 18:21 icudtl.dat
661012 -rwxr-xr-x 1 root root 243992 Aug 3 18:21 libEGL.so
661014 -rwxr-xr-x 1 root root 8948960 Aug 3 18:21 libGLESv2.so
661024 -rwxr-xr-x 1 root root 3103488 Aug 3 18:21 libffmpeg.so
661020 -rwxr-xr-x 1 root root 4488304 Aug 3 18:21 libvk_swiftshader.so
661018 -rwxr-xr-x 1 root root 8483376 Aug 3 18:21 libvulkan.so
792826 drwxr-xr-x 2 root root 4096 Aug 3 18:23 locales
792824 drwxr-xr-x 2 root root 4096 Aug 3 18:23 resources/app.asar
661015 -rw-r--r-- 1 root root 4791423 Aug 3 18:21 resources.pak
661009 -rw-r--r-- 1 root root 50592 Aug 3 18:21 snapshot_blob.bin
792821 drwxr-xr-x 2 root root 4096 Aug 3 18:23 swiftshader
661019 -rw-r--r-- 1 root root 170903 Aug 3 18:21 v8_context_snapshot.bin
661016 -rw-r--r-- 1 root root 107 Aug 3 18:21 vk_swiftshader_icd.json
[1] https://i.imgur.com/pGJ4Wvd.png