I am sorry for your loss.
If all of your mother's assets were in the trust, then you most likely will only have to file an income tax return for the trust (Form 1041) and, possibly, a final return (Form 1040) for your mother.
See https://www.irs.gov/publications/p559#en_US_2022_publink100099499
Note that the 1099-B you received may not reflect the correct basis for the mutual funds. The correct basis would be the fair market value on the date of death of your mother (May 14, 2022). Any gain or loss to be reported on Form 1041 would be calculated by subtracting that basis from the sales proceeds.
Also note that even if there is a loss on the sale of the mutual funds, that loss can be passed through to the beneficiaries (via K-1s) by filing a final 1041 for the trust.
