SEE BOLD
from multiple websites remarks similar to the following
However, given that FTX and BlockFi investors don’t currently know whether they will receive their investment back, or to what extent, it’s unclear what portion of their investment is completely and permanently ‘lost’. You should consult a crypto tax professional with questions on the specifics of your situation. in other words, the IRS doesn't like write-offs unless the security is totally worthless which seems to be unknown at this point.
Another option is to treat cryptocurrency lost to exchange bankruptcy as a casualty loss. However, these types of losses are considered non-deductible after the Tax Cuts & Jobs Act of 2017.
