Current listed version on PyPI is python >= 3.8 so it should install. You probably will only be able to run using CPython on Dynamo
Start by installing openseespy which will install in the C:\Users\%username%\AppData\Local\python-3.9.12-embed-amd64\Lib\site-packages folder - check this is which python Dynamo is using (sysconfig.get_path("data"))
You will also have to install 8.6 x64 Tcl/Tk (I used Magicsplat installer) which will install here → C:\Users\%username%\AppData\Local\Apps\Tcl86
If your embedded python is 3.9 you will have to edit the __init__.py file in the C:\Users\%username%\AppData\Local\python-3.9.12-embed-amd64\Lib\site-packages\openseespywin change line 14 to if 'Tcl86' in path:
Opensees loading in Dynamo Sandbox
import sys
from pathlib import Path
sys.path.append(str(Path.home().joinpath("AppData\\Local\\Apps\\Tcl86\\bin")))
import openseespy.opensees as ops
OUT = dir(ops)