As an employee who has a difficulty wearing a mask at workplace, especially if you are required to do so all day, you may be entitled to a reasonable accommodation under ADA or California FEHA. This is especially true if you suffer from acute asthma and associated difficulty breathing. The first step in this accommodation process should usually be approaching the employer and candidly discussing your difficulty working with a mask on and discussing possible solutions that could work for both sides. Like with other types of medical conditions and accommodations, this dialogue may require individualized assessment of the employer's needs and risks vs your challenges of being able to perform your job duties without having difficult breathing and/or aggravating your pre-existing respiratory illness.
I suspect that even when Covid-19 will be considered fully behind us, may workplaces will still require their employee to wear masks out of abundance of caution, so this issue is likely to be relevant for many years to come.