Big Business Change - Email Question For Namecheap + Squarespace Best Practices?

Hello all,

I am incorporated and have always used Google Workspace to manage everything, namecheap to host my domains, never Squarespace (always a bad idea in my experience - using a 3rd party). 

I'm shutting down a business and domain I have used for years. The secure domain forwarding is easy. Once I get the new domain live, the old is already associated and secure, so a redirect on the Namecheap side and I'm good. 

But, I will be closing one Google Workspace (for my old long time biz) and opening another (for the new biz). I have a lot of vendors under my long term email that I'm abandoning. I'm sure I'll miss a few people (in updating vendors). For any Namecheap + Squarespace vets, once I have closed the former Google Workspace, do I forward the old email via Namecheap or do I do add the old domain to my new Google Workspace account and forward it there? 

Fake example

Long term biz = mybiz.com with my email being bob@mybiz.com with a Squarespace site and a Google Workspace account to host the email and for other functions. 

I shut down mybiz.com and the corresponding Google Workspace account. 

My new biz  = epicnewbiz.com with my new email being bob@epicnewbiz.com with a Squarespace site and Google Workspace account to host this new email and other functions. 

Best Practices for forwarding bob@mybiz.com to my new bob@epicnewbiz.com is (a) do that at the Namecheap level or, (b) add my old domain and thus my old email to the new Google Workspace and forward from there? 

Thanks for your time and expertise, 
Bob

I also host domains on Namecheap and email on Google Workspace.

Suppose I shutdown the main site and create an email with a new domain. I will still renew the domain name every year (after all, it is quite cheap, only 10-12 $/year, Moreover, the main email, many customers still contact through there), then use Cloudflare Email Routing (free) to forward all new emails from old domain to new domain. 

Cloudflare has this feature recently.

Hey Tuan

Yeppers, I always keep the domains also to securely forward, but never had to abandon an email, so the Cloudflare is super helpful. Thank you!!!! Yest again, a rock star.