Why would you want to wear earplugs while singing?
Professional musicians nowadays tend to wear IEMs (In Ear Monitors), which are earplugs that drastically cut sound level but have an earbud driver that pipes in audio from the mixing board at a safer volume. This also offers better clarity, the ability for individual band members to hear themselves play better, and the possibility of a click track.
Despite the general public's lack of awareness of hearing safety, it's not really recommended that you even attend concerts without hearing protection (concert earbuds such as those from Etymotic Research) to attenuate the volume to safe levels, as venues are pushing 90-100db.
I went to a rather big multi-day outdoor rock show last year, and spent some time hanging out behind the FOH tent watching people work at various times because that's fun for me.
Hanging inside of the tent was a big, bright numeric LED display showing SPL, right by a big sternly-worded sign about the not-to-exceed level for the venue (which was, IIRC, 103dB).
For the headliners, I was regularly seeing 120dB -- and sometimes, 125dB -- presumably as measured somewhere around that point in space.
Choirs can get loud, too: I've read before that choir members can experience peaks of 110dB just from the sounds of their collective voices.
(Before IEMs became common, I worked extensively with a 5-piece band that had one aspect of their stage layout that they were absolutely unwilling to change, no matter how big or small that stage was: Each member had a "good" ear and a "bad" ear, and they considered it absolutely necessary to never be positioned so that their good ear was facing the drummer.)
It's maybe less significant for choir compared to e.g. rock band with amps or wind band with tons of brass, but you can still get ear damage. (That's where I got my tinnitus from lol)
They do make specialized earplugs for music that allow some amount of pass-through, and don't isolate as much.
Protect those ears!