Dear @chiara,
Thank you for your message.
We noticed that you had the same issue in 2021.
A workaround was proposed in the previous thread Issues with Sen2Cor v2.9 user guide DEM reference - #11 by chiara proposed in Processing Error due to SRTM Data Conflict - #6 by vicencpala .
You could try this and let us know. This problem seems to only happen on Windows machines. Does it happen for every try you make ?
In addition you may want to have a look to Frequently Asked Questions point #2 about the Copernicus DEM support that is more accurate than the former SRTM DEM and check if you experience the same kind of error.
Cheers,
@Sen2cor_dev_team