OK, today, before trying the steps suggested in the previous messages,
I did an update. FWIW, this is what came:
Get:2
http://www.deb-multimedia.org sid/main amd64 libavutil56 amd64
10:4.2.1-dmo1 [272 kB]
Get:1
http://cdn-fastly.deb.debian.org/debian sid/main amd64 libisl21
amd64 0.21-2 [595 kB]
Get:33
http://www.deb-multimedia.org sid/main amd64 libswresample3
amd64 10:4.2.1-dmo1 [91.8 kB]
Get:34
http://www.deb-multimedia.org sid/main amd64 libavcodec58 amd64
10:4.2.1-dmo1 [4,896 kB]
Get:3
http://cdn-fastly.deb.debian.org/debian sid/main i386 gcc-9-base
i386 9.2.1-8 [193 kB]
Get:4
http://cdn-fastly.deb.debian.org/debian sid/main amd64
gcc-9-base amd64 9.2.1-8 [193 kB]
Get:5
http://cdn-fastly.deb.debian.org/debian sid/main i386 libstdc++6
i386 9.2.1-8 [535 kB]
Get:6
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libstdc++6 amd64 9.2.1-8 [501 kB]
Get:7
http://cdn-fastly.deb.debian.org/debian sid/main i386 libgomp1
i386 9.2.1-8 [93.0 kB]
Get:50
http://www.deb-multimedia.org sid/main amd64 libavformat58
amd64 10:4.2.1-dmo1 [1,004 kB]
Get:8
http://cdn-fastly.deb.debian.org/debian sid/main amd64 libgomp1
amd64 9.2.1-8 [88.1 kB]
Get:9
http://cdn-fastly.deb.debian.org/debian sid/main amd64 libgcc1
amd64 1:9.2.1-8 [40.5 kB]
Get:51
http://www.deb-multimedia.org sid/main amd64 libavresample4
amd64 10:4.2.1-dmo1 [89.0 kB]
Get:52
http://www.deb-multimedia.org sid/main amd64 libpostproc55
amd64 10:4.2.1-dmo1 [89.8 kB]
Get:53
http://www.deb-multimedia.org sid/main amd64 libswscale5 amd64
10:4.2.1-dmo1 [190 kB]
Get:54
http://www.deb-multimedia.org sid/main amd64 libavfilter7 amd64
10:4.2.1-dmo1 [1,460 kB]
Get:10
http://cdn-fastly.deb.debian.org/debian sid/main i386 libgcc1
i386 1:9.2.1-8 [48.0 kB]
Get:11
http://cdn-fastly.deb.debian.org/debian sid/main i386
libatomic1 i386 9.2.1-8 [9,528 B]
Get:12
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libatomic1 amd64 9.2.1-8 [9,016 B]
Get:55
http://www.deb-multimedia.org sid/main amd64 libavdevice58
amd64 10:4.2.1-dmo1 [104 kB]
Get:56
http://www.deb-multimedia.org sid/main amd64 ffmpeg amd64
10:4.2.1-dmo1 [1,486 kB]
Get:13
http://cdn-fastly.deb.debian.org/debian sid/main amd64 libcc1-0
amd64 9.2.1-8 [47.8 kB]
Get:14
http://cdn-fastly.deb.debian.org/debian sid/main amd64 libitm1
amd64 9.2.1-8 [27.6 kB]
Get:57
http://www.deb-multimedia.org sid/main amd64 vlc amd64
1:3.0.8-dmo2 [63.5 kB]
Get:58
http://www.deb-multimedia.org sid/main amd64
vlc-plugin-video-output amd64 1:3.0.8-dmo2 [190 kB]
Get:59
http://www.deb-multimedia.org sid/main amd64 vlc-plugin-base
amd64 1:3.0.8-dmo2 [2,832 kB]
Get:15
http://cdn-fastly.deb.debian.org/debian sid/main amd64 libasan5
amd64 9.2.1-8 [390 kB]
Get:16
http://cdn-fastly.deb.debian.org/debian sid/main amd64 liblsan0
amd64 9.2.1-8 [136 kB]
Get:17
http://cdn-fastly.deb.debian.org/debian sid/main amd64 libtsan0
amd64 9.2.1-8 [295 kB]
Get:18
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libubsan1 amd64 9.2.1-8 [128 kB]
Get:19
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libquadmath0 amd64 9.2.1-8 [144 kB]
Get:20
http://cdn-fastly.deb.debian.org/debian sid/main amd64 g++-9
amd64 9.2.1-8 [9,784 kB]
Get:21
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libstdc++-9-dev amd64 9.2.1-8 [1,693 kB]
Get:22
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libgcc-9-dev amd64 9.2.1-8 [2,345 kB]
Get:23
http://cdn-fastly.deb.debian.org/debian sid/main amd64 gcc-9
amd64 9.2.1-8 [9,366 kB]
Get:24
http://cdn-fastly.deb.debian.org/debian sid/main amd64 cpp-9
amd64 9.2.1-8 [8,900 kB]
Get:25
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libgfortran5 amd64 9.2.1-8 [634 kB]
Get:26
http://cdn-fastly.deb.debian.org/debian sid/main i386
liblcms2-2 i386 2.9-4 [156 kB]
Get:27
http://cdn-fastly.deb.debian.org/debian sid/main amd64
liblcms2-2 amd64 2.9-4 [146 kB]
Get:28
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libatspi2.0-dev amd64 2.34.0-1 [65.7 kB]
Get:29
http://cdn-fastly.deb.debian.org/debian sid/main amd64
gir1.2-atspi-2.0 amd64 2.34.0-1 [21.4 kB]
Get:30
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libatspi2.0-0 amd64 2.34.0-1 [69.9 kB]
Get:31
http://cdn-fastly.deb.debian.org/debian sid/main amd64
at-spi2-core amd64 2.34.0-1 [71.9 kB]
Get:32
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libatk1.0-dev amd64 2.34.0-1 [89.7 kB]
Get:35
http://cdn-fastly.deb.debian.org/debian sid/main amd64
gir1.2-atk-1.0 amd64 2.34.0-1 [25.8 kB]
Get:36
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libatk1.0-data all 2.34.0-1 [146 kB]
Get:37
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libatk1.0-0 amd64 2.34.0-1 [51.3 kB]
Get:38
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libatk-bridge2.0-dev amd64 2.34.0-1 [9,184 B]
Get:39
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libatk-bridge2.0-0 amd64 2.34.0-1 [63.0 kB]
Get:40
http://cdn-fastly.deb.debian.org/debian sid/main i386 libsoxr0
i386 0.1.3-1 [79.2 kB]
Get:41
http://cdn-fastly.deb.debian.org/debian sid/main amd64 libsoxr0
amd64 0.1.3-1 [77.5 kB]
Get:42
http://cdn-fastly.deb.debian.org/debian sid/main amd64
liblcms2-utils amd64 2.9-4 [47.6 kB]
Get:43
http://cdn-fastly.deb.debian.org/debian sid/main amd64 libltc11
amd64 1.3.1-1 [14.0 kB]
Get:44
http://cdn-fastly.deb.debian.org/debian sid/main amd64
wine-development all 4.10-1 [139 kB]
Get:45
http://cdn-fastly.deb.debian.org/debian sid/main amd64
wine64-development amd64 4.10-1 [299 kB]
Get:46
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libwine-development amd64 4.10-1 [24.8 MB]
Get:47
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libwxbase3.0-0v5 amd64 3.0.4+dfsg-12 [1,090 kB]
Get:48
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libwxgtk3.0-0v5 amd64 3.0.4+dfsg-12 [4,525 kB]
Get:49
http://cdn-fastly.deb.debian.org/debian sid/main amd64
libwxgtk3.0-gtk3-0v5 amd64 3.0.4+dfsg-12 [4,494 kB]
In any event, now with DMO repos, apt only want to remove 11 packages
(same as without) without any action on my part:
The following packages will be REMOVED:
kde-style-breeze-qt4 libavcodec58:i386 libavutil56:i386
libfaudio0:i386 libmfx1:i386 libomp5-7 libswresample3:i386
libwine-development:i386 pylint3 python-logilab-common wine32-development:i386
I could tell that I could let kde-style-breeze-qt4,libomp5-7,
python-logilab-common and pylint3 go, so I removed them. I still see
some of the DMO packages marked to be removed (libavcodec58:i386,
libavutil56:i386, libmfx1:i386...), but I assume is the usual Sid
thing where you just need to wait for new updates to come to get
resolved. (I can see that libmfx1 wants to go from 1.25-dmo1 to
19.2.1-1 (from Debian's official repo), for instance.) Let me know if
I am wrong about just waiting. Otherwise I think the issue has been
resolved.
Thanks all for your help!