There are a couple of well-supported Telnet programs you could use. A common one is SyncTerm which is purpose-built for the BBS scene (also is free). Zoc is another popular one, but it is more designed as a general-purpose terminal emulator (great for SSH-ing into servers). Zoc is commercial software.

SyncTerm: https://syncterm.bbsdev.net/ Zoc: https://www.emtec.com/zoc/index.html