Experimenting is good but you are overthinking and making it difficult.
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Simply download Raspberry Pi OS Lite (64bit) Bullseye and copy it to your SD card / hard drive.
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You can copy the image to your SD / hard drive using the terminal or if you prefer a GUI via balena etcher or the official Raspberry imager.
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The benefit of the Raspberry imager is that it is able to download the image for you, can enable SSH easily within the options (a must do unless you have a screen and keyboard connected to your raspberry), and lets you choose a different name instead of pi.
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Put SD card inside / connect hard drive and boot it up.
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SSH into your server, execute the command
$ wget https://install.yunohost.org/bullseye -O install_script
$ bash install_script -d testing
and follow the instructions. There is nothing else to it.
No need to worry about architecture or anything else. No need to change/modify/edit anything.
Some more detailed instructions by @mcb13 can be found here (pay attention, they are using Buster).