The way I would look at it is the severity. How severe is the COVID-19 case where you are? How safe do you feel, even with the masks? Do the Mosques in your area follow the COVID-19 guidelines? Do the people socially distance themselves, avoid physical contact, and wear masks?
The Mosques that I've been to do the following:
The largest and central Mosque in my state:
A) Completely stripped the carpet and only left 6 ft markers in intervals
B) Closed the bathrooms (for some reason)
C) Limit to a certain amount of people from entering.
D) Mandate masks
A smaller Mosque does the following:
A) Order people to pray 6 feet apart (though unfortunately due to the size, people cannot fully social distance but try their best)
B) Mandate masks
C) Allow people to pray outside as well
My least favorite experience would be this Mosque I visited out of state:
A) Had someone check your temperature upon entry
B) Mandated masks
C) DID NOT SOCIAL DISTANCE
I'm not too familiar with a plague/pandemic during the Prophet's time, but Allah advises us to never put ourselves in danger of our health.
As long as the Masjids are strict on social distancing measures and mask mandates, there should be no problem. It's best if they take it seriously, similarly, with the first Mosque I listed along with having your temperature checked. Prophet Muhammad (saws) encouraged Muslims to go to the Masjid, so as long as they are opened and are following health and safety guidelines, Insha'Allah there is nothing to be worried about.
HOWEVER, if a Masjid fails and ignores these protocols to keep people safe, it's best to talk to the owner/management and address your concerns and/or go to a different Mosque.
If grocery stores, restaurants, movie theatres, churches, etc. are all open, why can't Masjids? The government/president or whoever believes that these places can open back up again for a reason. If they didn't find it safe enough, they would hold back and quarantine people longer.
If you have a weak immune system, it's up to you. Do you feel comfortable with the way your local Mosque is handling the COVID-19 guidelines? If so, do your best to visit the house of Allah and pray. If not, speak up about it because we as Muslims must also do our part to prevent the spread of this disease, even if we've made it accustomed to our lives.