CocoaPods trunk no Specs

I installed Cocoapods v1.7.0 on Mac Catalina 10.15.7 (19H2). Now I'm upgrading Cocoapods to v1.10.0.

Firstly I uninstall v1.7.0 following https://superuser.com/a/686319.

Then install v1.10.0 with no issue:

sudo gem install cocoapods

In my project folder, I run pod repo update:

$pod repo update                    ✔  6s  17:17:13 
Updating spec repo `trunk`

$pod repo update                    ✔  3s  17:34:21

It only takes 3s with no issue, but I get nothing in folder ~/.cocoapods/repos/trunk/Specs(empty folder):(

Then as you may already know it cannot find any spec when running pod install:

pod install --repo-update
Updating local specs repositories
Adding spec repo `trunk` with CDN `https://cdn.cocoapods.org/`
Analyzing dependencies
[!] Unable to find a specification for `Firebase/Analytics`

You have either:
 * mistyped the name or version.
 * not added the source repo that hosts the Podspec to your Podfile.

Note: Not pod Firebase/Analytics issue, tried other pods also got this error.

Any suggestion to fetch Cococapods CDN trunk Specs normally? Thanks in advance.