I'm simply trying to push my Flask app to Heroku but I encountered the following error:

remote:            ERROR: Command errored out with exit status 1:
remote:             command: /app/.heroku/python/bin/python -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-qq0uk569/xlwings/setup.py'"'"'; __file__='"'"'/tmp/pip-install-qq0uk569/xlwings/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base /tmp/pip-pip-egg-info-dxixzzkg
remote:                 cwd: /tmp/pip-install-qq0uk569/xlwings/
remote:            Complete output (5 lines):
remote:            Traceback (most recent call last):
remote:              File "<string>", line 1, in <module>
remote:              File "/tmp/pip-install-qq0uk569/xlwings/setup.py", line 32, in <module>
remote:                raise OSError("xlwings requires an installation of Excel and therefore only works on Windows and macOS. To enable the installation on Linux nevertheless, do: export INSTALL_ON_LINUX=1; pip install xlwings")
remote:            OSError: xlwings requires an installation of Excel and therefore only works on Windows and macOS. To enable the installation on Linux nevertheless, do: export INSTALL_ON_LINUX=1; pip install xlwings
remote:            ----------------------------------------
remote:        ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output.
remote:  !     Push rejected, failed to compile Python app.
remote: 
remote:  !     Push failed
remote: Verifying deploy...
remote: 
remote: !       Push rejected to browebgen.
remote: 
To https://git.heroku.com/browebgen.git! [remote rejected] main -> main (pre-receive hook declined)
error: failed to push some refs to 'https://git.heroku.com/browebgen.git'

I'm not sure what I need to do to get rid of this error.

The error message says it all:

xlwings requires an installation of Excel and therefore only works on Windows and macOS. To enable the installation on Linux nevertheless, do: export INSTALL_ON_LINUX=1; pip install xlwings

You might be using a package in your app named xlwings which is built to be used on Windows and Mac but the servers on Heroku have linux installed on them so you'll first have to set an environment variable INSTALL_ON_LINUX to 1 then try to deploy the app again.

From the Heroku CLI you can do:

heroku config:set INSTALL_ON_LINUX=1