To anyone who face that issue - check your php.ini: curl.cainfo must have the valid chained certificate from https://curl.se/docs/caextract.html. I updated it to the latest and after that I was able to successfully connect PayPal and open Themes Catalog.
Here is my /etc/php.ini:
[curl] ; A default value for the CURLOPT_CAINFO option. This is required to be an ; absolute path. curl.cainfo = /etc/ssl/certs/cacert-2025-08-12.pem