I just got the update to version 20.4.2+2.1 on Linux Mint 19 XFCE. I have been using the QT4 version because it honors the option "Use the system native dialog" which in my case would be the
GTK dialog. This latest version does not honor that option and instead uses the QT dialog.
I tried the QT5 version when it first came out and it also had this problem. Anyway, I thought I would take this opportunity and switch to the QT5 version (also Smtube) and get rid of all the QT4 stuff. The QT5 version still uses the QT open dialog but I can live with that.
I have been using the QT5 version on Debian Testing XFCE for a few months now and it does honor the option "Use the system native dialog" and uses the GTK dialog. Even this latest version of
Smplayer. Perhaps this has to do with the older QT version on Linux Mint. 5.9 vs 5.12.5 on Debian. I suppose I will find out when Linux Mint 20 comes out later this year.
Anyway, no big deal. Just thought I'd mention it.