Issue is because of open vsx CORS request as mentioned here Searching the extension marketplace fails with CORS error · Issue #128583 · microsoft/vscode · GitHub
Solution: There is temporary workaround:
in the file ~/.vscode-oss/argv.json
add the line: "enable-browser-code-loading": false
Reference: [1.58] Extension marketplace not working · Issue #746 · VSCodium/vscodium · GitHub