Is it possible to have 1 slave server with multiple master?

Here is my set of master server:
DbServer1 – 10.1.0.1
DbServer2 – 10.1.0.2
DbServer3 – 10.1.0.3
DbServer4 – 10.1.0.4

and my replica server would be on 10.1.0.5

Is this doable if I create 4 instances of MySQL on a single server with different ports? But keeping in mind that all of my Master are using the default port which is 3306

Yes, you can run on different port and configure replication through master.
If you have different table name or db name in all master, you can for with multi source replica in that case you just need to install single instance for replica node of all masters. You can go through here and comment if have any doubt and need more clarification.

Multi-source (or MariaDB multi-source) allows for master servers to one replica.

Yes multiple instances are possible on a single server if they have distinct ports and data directories.