One of the qualities of Lord Vishnu is that of being 'sarvagnyan' which means all knowing or omniscient. He does not need to see your face to know who you are, being all knowing, He would very much be aware of your visit to His temple. You need not therefore worry that he would not recognize you because of your mask.
This is unprecedented times when we are facing a pandemic and when our lives are in danger. That is, we are going through an emergency situation (Apatkala). And scriptures say that when there is an emergency, Dharma Acharana (performance of religious duties) must take a backseat.
So you need not worry about not being able to perform the Darshana in the most ...
अज्ञो वदति विष्णाय सुज्ञो वदति विष्णवे |
द्वयोः सदृशं पुण्यं भावग्राहि जनार्दनः ||
murkho vadati visnaya dhiro vadati visnave |
ubhayos tu samam punyam 𝙗𝙝𝙖𝙫𝙖-𝙜𝙧𝙖𝙝𝙞 𝙟𝙖𝙣𝙖𝙧𝙙𝙖𝙣𝙖𝙝||
The purport is that any service or offering done to Bhagavan Vishnu, He accepts the mood in which they are offered.