Option 1: This is preferred as once you leave your employer, they will withdraw your H1B which is the basis of H4 EOS & EAD applications. This may cause the H4/EAD to be denied. USCIS may or may not send an RFE to submit the copy of H1B I-797 approval notice with the new employer and that is what will create uncertainty for H4/EAD approval.
Option 2: You can interfile the copy of new H1B I-797 approval notice to your pending H4/EAD applications however you will not receive any receipt for the interfile. That way USCIS will have the most updated I-797 for the primary H1B and your H4/EAD applications will not be impacted even if the current employer will withdraw your H1B once you leave.
Option 3: You can extend the H4 I-94 using your current H1B approval (April 2025) by travelling to Mexico border before you apply for H1B transfer with another employer. That way the H4 will be extended up to April 2025. Once your I-94 is extended, you can send the copy to USCIS address processing your EAD. Also this way you get 180 days automatic extension of the EAD and your H4 spouse can keep working even after the EAD expiry of April 2022.
Read below articles carefully.
https://www.am22tech.com/usa/news/h4-l2-ead-auto-extension-uscis-policy-change/
Ideally you will apply H4 EOS and EAD along with the H1B transfer. Of course the H4/EAD applications will need to reach USCIS before the current expiry.