This happens because nodejs in bionic is linked against OpenSSL 1.0 (see #1779863) while most other packages in bionic use OpenSSL 1.1. Installing any package using OpenSSL 1.1 will conflict with nodejs (more exactly: any package depending on libssl-dev, which conflicts with libssl1.0-dev).
As Esko noted, bionic has some other packages conflicting because of this OpenSSL 1.0+1.1 mix.
This happens because nodejs in bionic is linked against OpenSSL 1.0 (see #1779863) while most other packages in bionic use OpenSSL 1.1. Installing any package using OpenSSL 1.1 will conflict with nodejs (more exactly: any package depending on libssl-dev, which conflicts with libssl1.0-dev).
As Esko noted, bionic has some other packages conflicting because of this OpenSSL 1.0+1.1 mix.