401k loss deduction

Gains or losses within a 401(k) tax deferred retirement account are not reported on a tax return. 

If you made a withdrawal from the account then you would be receiving a Form 1099-R and that is reported on a tax return.

What do you mean by "materialized investment loss"?  

1. Did you cash out your 401(k) account and the proceeds were less than you contributed?

2. Is your 2022 year-end balance less than your 2021 year-end balance?

3. Is this a Roth 401(k) account whose balance has declined?

since investment gains and other income aren't taxed, declines in market value and losses aren't deductible.