This guide assumes any arch based distribution for the sake of simplicity (but anything x86_64/glib should work), tested setups include Artix Linux and Gentoo.
Quick setup below makes use of various wrappers provided in this repository making setup somehow consistent, even on fresh installs.
That doesn't mean you have to use them as it's mostly automatization and integration of proton without steam.

1. Guide will use LDJ-20210915 for setup, if you are unsure of what you are doing, that's the recommended version to follow with
2. Guide will use /var/games/ as starting directory for installation and expects game at /var/games/iidx/LDJ-20210915, therefore this step has to be completed if not done before

sudo usermod -aG games $USER
# restart system (or relogin user)
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3. Get everything listed in requirements, if you are unsure of what you are doing, below commands should be equal to completing this step (other than installing steam)

mkdir -p /var/games/iidx/requirements
##    common system libraries utilized in wine    ##
# Follow steps from https://github.com/lutris/docs/blob/master/WineDependencies.md#archendeavourosmanjaroother-arch-derivatives
##    automatization utils (skip if you have your own setup in mind)
cd /var/games/iidx
git clone https://codeberg.org/nixac/automatization --recurse-submodules
sudo pacman -S jq
##    proton ge (includes patching)    ##
cd /var/games/iidx/requirements
wget https://github.com/GloriousEggroll/proton-ge-custom/releases/download/GE-Proton8-16/GE-Proton8-16.tar.gz
tar -xf GE-Proton8-16.tar.gz
mv GE-Proton8-16 proton-ge-8.16
cd proton-ge-8.16
patch -p1 < /var/games/iidx/automatization/proton.patch
cp /var/games/iidx/automatization/0005731108.py protonfixes/gamefixes/
##    pipewire (recommended to follow guide for distribution you use instead)    ##
sudo pacman -S pipewire pipewire-pulse pipewire-jack pipewire-alsa wireplumber gst-plugin-pipewire
systemctl --user enable pipewire pipewire-pulse wireplumber
systemctl --user start pipewire pipewire-pulse wireplumber
sudo usermod -aG realtime,audio $USER
# restart system (or relogin user)
##    get all custom requirements (most likely what you are missing)    ##
cd /var/games/iidx/requirements
wget https://codeberg.org/nixac/spicetools/releases/download/v0.1.0_2023-09-29/spicetools.tar.gz
mkdir spicetools
tar -xf spicetools.tar.gz -C spicetools
git clone https://codeberg.org/nixac/bmsound_wine --recurse-submodules
cd bmsound_wine
make -Rs build TARGET_ARCH=x64 TARGET_TYPE=Release
mv bin/Release/x64 ../bmsw
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4. This is how your /var/games/iidx should look like by now, you may safely delete any directories not listed here

- /var/games/iidx/automatization
- /var/games/iidx/requirements/proton-ge-8.16
- /var/games/iidx/requirements/spicetools
- /var/games/iidx/requirements/bmsw
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5. Link /var/games/iidx/.steam to steam's game library, in this case we assume you use single library (so how default steam installation works)

cd "/var/games/iidx"
ln -sfn $HOME/.steam .steam
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6. Add game (in this case LDJ-20210915) and proton-ge to your library (in this case proton-ge-8.16), for person following step-by-step this would be a correct command

mv "/var/games/iidx/LDJ-20210915" "/var/games/iidx/.steam/root/steamapps/common/Beatmania IIDX 28"
mv "/var/games/iidx/requirements/proton-ge-8.16" "/var/games/iidx/.steam/root/steamapps/common/proton-ge-8.16" 
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7. Move all .dll files from contents to contents/modules if this isn't the case already, this should already be the case for LDJ-20210915

mv "/var/games/iidx/.steam/root/steamapps/common/Beatmania IIDX 28/contents/"*.dll "/var/games/iidx/.steam/root/steamapps/common/Beatmania IIDX 28/contents/modules/"
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8. Add bmsound_wine (audio solution for wine) and spicetools (wine fork) to game's dump, for person following step-by-step this would be a correct command

mv "/var/games/iidx/requirements/bmsw/bmsound-"* "/var/games/iidx/.steam/root/steamapps/common/Beatmania IIDX 28/contents/modules/"
mv "/var/games/iidx/requirements/spicetools/spice"* "/var/games/iidx/.steam/root/steamapps/common/Beatmania IIDX 28/contents/"
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9. Apply wine patches through provided patcher if there are any (do not enable wasapi shared patch), in case of LDJ-20210915 you need a Bistrover specific fix
10. Set your monitor to target refresh rate (so 120hz for this guide), example below assumes you want game on main monitor

xrandr
# replace device (--output) with output of command above at line like this "DP-0 connected primary ....", where you would replace "DP-0" with the one listed in your output
# replace resolution (--mode) with your native resolution, you don't need to target specific resolution (as long as ratio is correct)
xrandr --output DP-0 --mode 1920x1080 --rate 120
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11. Run ep_bm2dxnix to setup prefix and start spicetools config, if you followed step-by-step until now, this should be enough

/var/games/iidx/automatization/ep_bm2dxnix 28 --cfg
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12. After you are done close config tool and run ep_bm2dxnix again to start the game, if you followed step-by-step until now, this should be enough

/var/games/iidx/automatization/ep_bm2dxnix 28
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13. If everything worked you can safely delete /var/games/iidx/requirements/, but know that you will probably need to rebuild bmsound_wine on bigger system updates
14. You can check advanced setup for further/optional setup steps