Thanks @furas for the hint: simply uninstalling qt6-main using `conda remove qt6-main` worked for me (conda installed/uninstalled a lot of other packages, unfortunately I didn't really paid attention and just clicked ok). Just in case someone is interested: that's what my environment looks now:
_openmp_mutex 4.5 2_gnu conda-forge
ampl-asl 1.0.0 he0c23c2_2 conda-forge
brotli-python 1.0.9 py312h5da7b33_9
bzip2 1.0.8 h2466b09_7 conda-forge
ca-certificates 2025.2.25 haa95532_0
cairo 1.16.0 hc68a040_5
colorama 0.4.6 pyhd8ed1ab_1 conda-forge
contourpy 1.3.1 py312h214f63a_0
cycler 0.11.0 pyhd3eb1b0_0
deepdiff 8.1.1 pyhd8ed1ab_0 conda-forge
double-conversion 3.3.1 he0c23c2_0 conda-forge
expat 2.6.4 h8ddb27b_0
font-ttf-dejavu-sans-mono 2.37 hd3eb1b0_0
font-ttf-inconsolata 2.001 hcb22688_0
font-ttf-source-code-pro 2.030 hd3eb1b0_0
font-ttf-ubuntu 0.83 h8b1ccd4_0
fontconfig 2.14.1 hb33846d_3
fonts-anaconda 1 h8fa9717_0
fonts-conda-ecosystem 1 hd3eb1b0_0
fonttools 4.55.3 py312h827c3e9_0
freetype 2.13.3 h0620614_0
geojson 3.2.0 pyhd8ed1ab_0 conda-forge
glib 2.78.4 hd77b12b_0
glib-tools 2.78.4 hd77b12b_0
graphite2 1.3.14 hd77b12b_1
harfbuzz 10.2.0 hf458a27_0
icu 73.1 h6c2663c_0
intel-openmp 2024.2.1 h57928b3_1083 conda-forge
ipopt 3.14.17 h905d1ba_0 conda-forge
jpeg 9e h827c3e9_3
kiwisolver 1.4.8 py312h5da7b33_0
krb5 1.21.3 hdf4eb48_0 conda-forge
lcms2 2.16 hb4a4139_0
lerc 4.0.0 h5da7b33_0
libblas 3.9.0 26_win64_mkl conda-forge
libcblas 3.9.0 26_win64_mkl conda-forge
libclang13 14.0.6 default_h8e68704_2
libdeflate 1.22 h5bf469e_0
libexpat 2.6.4 he0c23c2_0 conda-forge
libffi 3.4.2 h8ffe710_5 conda-forge
libflang 5.0.0 h6538335_20180525 conda-forge
libgcc 14.2.0 h1383e82_2 conda-forge
libglib 2.78.4 ha17d25a_0
libgomp 14.2.0 h1383e82_2 conda-forge
libhwloc 2.11.2 default_ha69328c_1001 conda-forge
libiconv 1.17 hcfcfb64_2 conda-forge
libintl 0.22.5 h5728263_3 conda-forge
libjpeg-turbo 2.0.0 h196d8e1_0
liblapack 3.9.0 26_win64_mkl conda-forge
liblzma 5.6.3 h2466b09_1 conda-forge
libpng 1.6.39 h8cc25b3_0
libpq 12.15 h906ac69_0
libsqlite 3.48.0 h67fdade_1 conda-forge
libtiff 4.5.1 h44ae7cf_1
libwebp-base 1.5.0 h3b0e114_0 conda-forge
libwinpthread 12.0.0.r4.gg4f2fc60ca h57928b3_9 conda-forge
libxcb 1.17.0 h0e4246c_0 conda-forge
libxml2 2.13.5 h24da03e_0
libxslt 1.1.41 h0739af5_0
libzlib 1.2.13 h2466b09_6 conda-forge
llvm-meta 5.0.0 0 conda-forge
llvmlite 0.44.0 py312h8b1c7eb_1
lxml 5.3.0 py312h395c83e_1
lz4-c 1.9.4 h2bbff1b_1
matplotlib 3.10.1 py312h2e8e312_0 conda-forge
matplotlib-base 3.10.1 py312h90004f6_0 conda-forge
minizip 4.0.3 hb68bac4_0
mkl 2024.2.2 h66d3029_15 conda-forge
mumps-seq 5.7.3 h7c2359a_6 conda-forge
networkx 3.4.2 pyh267e887_2 conda-forge
numba 0.61.0 py312hcccf92d_1 conda-forge
numpy 2.1.3 py312h49bc9c5_0 conda-forge
openjpeg 2.5.2 hae555c5_0
openmp 5.0.0 vc14_1 conda-forge
openssl 3.4.0 ha4e3fda_1 conda-forge
orderly-set 5.2.3 pyh29332c3_1 conda-forge
packaging 24.2 pyhd8ed1ab_2 conda-forge
pandapower 3.0.0 pyhd8ed1ab_0 conda-forge
pandas 2.2.3 py312h72972c8_1 conda-forge
pcre2 10.42 h0ff8eda_1
pillow 11.1.0 py312h096bfcc_0
pip 25.0 pyh8b19718_0 conda-forge
pixman 0.44.2 had0cd8c_0 conda-forge
ply 3.11 pyhd8ed1ab_3 conda-forge
pthread-stubs 0.3 h3c9f919_1
pyomo 6.8.2 py312h275cf98_1 conda-forge
pyparsing 3.2.0 py312haa95532_0
pyside6 6.7.2 py312hf8997a8_0
python 3.12.3 h2628c8c_0_cpython conda-forge
python-dateutil 2.9.0.post0 pyhff2d567_1 conda-forge
python-tzdata 2025.1 pyhd8ed1ab_0 conda-forge
python_abi 3.12 5_cp312 conda-forge
pytz 2024.1 pyhd8ed1ab_0 conda-forge
qhull 2020.2 h59b6b97_2
qtbase 6.7.2 h0804d20_0
qtdeclarative 6.7.2 h5da7b33_0
qtshadertools 6.7.2 h5da7b33_0
qtsvg 6.7.2 hf2fb9eb_0
qttools 6.7.2 h0de5f00_0
qtwebchannel 6.7.2 h5da7b33_0
qtwebengine 6.7.2 h601c93c_0
qtwebsockets 6.7.2 h5da7b33_0
scipy 1.13.1 py312h1f4e10d_0 conda-forge
setuptools 75.8.0 pyhff2d567_0 conda-forge
six 1.17.0 pyhd8ed1ab_0 conda-forge
sqlite 3.45.3 h2bbff1b_0
tbb 2021.13.0 h62715c5_1 conda-forge
tk 8.6.13 h5226925_1 conda-forge
tornado 6.4.2 py312h827c3e9_0
tqdm 4.67.1 pyhd8ed1ab_1 conda-forge
typing_extensions 4.12.2 py312haa95532_0
tzdata 2025a h78e105d_0 conda-forge
ucrt 10.0.22621.0 h57928b3_1 conda-forge
unicodedata2 15.1.0 py312h827c3e9_1
vc 14.42 haa95532_4
vc14_runtime 14.42.34433 h6356254_24 conda-forge
vs2015_runtime 14.42.34433 hfef2bbc_24 conda-forge
wheel 0.45.1 pyhd8ed1ab_1 conda-forge
xorg-libxau 1.0.12 h0e40799_0 conda-forge
xorg-libxdmcp 1.1.5 h0e40799_0 conda-forge
xz 5.6.4 h4754444_1
zlib 1.2.13 h2466b09_6 conda-forge
zstd 1.5.6 h8880b57_0