See https://winscp.net/eng/docs/ui_login#defaults

Atm, we do not recommend using TLS 1.3. There are still interoperability problems, as it is a new thing in FTP world. That's why it is disabled by default. Once it becomes stable, we will enable it by default (in future release).
https://winscp.net/tracker/1834

Hello,

It would be a nice feature if I could set a default configuration for new connection profiles in WinSCP, e.g. set min TLS to 1.2 and max TLS to 1.3 or a default ssh key.

If this feature already exists, I didn't find it, sorry.