I don’t usually need that feature, so your comment prompted me to try after a long time … and it didn’t work for me either, but it clearly did in the past. So …
I’m using Windows 10 Pro 1903.
For testing purposes over time I apparently installed different USB/MTP/ADB driver packages like “Minimal ADB and Fastboot” (I think there are even different incarnations with the same name), “Universal ADB Driver” and possibly more, and I either forgot to uninstall them again, or they didn’t uninstall cleanly, or whatever.
To get MTP running again, I did the following …
- Disconnected the phone from the computer.
- In Control Panel - Programs and Features:
Uninstalled everything with “MTP” or “ADB” in its name. - Rebooted Windows.
- In Control Panel - Device Manager:
Enabled View - Show hidden devices, and then uninstalled every possible ADB, MTP and smartphone device, hidden or not. - Rebooted Windows.
- Connected the phone again with booted TWRP, Windows then needed a moment to set up MTP again automatically and prompted a success message afterwards.
Et voilà … Now the Fairphone 2 with “Internal Storage” and “Micro SD card” shows up again in Explorer as soon as TWRP is booted and the phone is connected via USB. I tried TWRP 3.2.3-0 and 3.3.1-0.
…
Turns out I deleted my working dic:adb and dic:fastboot commands with this endeavour (they were probably from Minimal ADB and Fastboot), so I did the following …
- Downloaded the current Android SDK Platform Tools, it’s better to use these anyway.
- Unzipped the ZIP file to C:\platform-tools (you can unzip it to wherever you like).
- Added this path to the Windows “PATH” environment variable, so adb and fastboot could be run from everywhere again without always having to prefix them with
C:\platform-tools\.