H4 visa extension denied after 300 days of I-94 expiry (H1B is valid till 2023)

[alexvisa]

USCIS has denied H4 visa extension for my dependents although my H1B is valid until March 2023.

Timeline:
H4 Extension filed on 02 Jun 2020 along with H1B extension for the Primary applicant
H4 I-94 expired on 10 Jul 2020
Biometrics completed for H4 extension in Aug
H1B extension approved in Jul 2020 with validity till Mar 2023 (I-140 approved already)
H4 extension denied on 30th Apr 2021

It's already 300 days since H4 I-94 expired. Is there any way to appeal this decision?
How long can my dependents stay in the US legally without getting banned for 3yrs for overstay?

[newacct]

Why was it denied?

They only start accruing unlawful presence from the date of the denial (and only those who are 18 or above accrue unlawful presence). As long as they leave within 180 days of the denial, they won't trigger a ban. However, if they don't leave or file a motion within 33 days of the denial, USCIS might issue a Notice to Appear for removal proceedings, so it's best to leave or file a motion to reopen or reconsider within a month.

[rkk09]

Hi,
Better if they leave country as soon as possible would be really avoiding such kind of issues.. And just try to get H4 visa at consulate once Consulate offices are stated accepting visa appointments.
Thanks