I have tried 'cpan install LWP::UserAgent::https', but it seemed didn't work. Then i tried to force it with 'cpan install -fi LWP::UserAgent::https'. It said 'make install --OK'.

Note that the distribution name is LWP::Protocol::https, not LWP::UserAgent::https, which does not exist.

That most likely means that "installing" the module failed its tests for some reason, but you decided to paper over the failure.

A better approach is to look at the installation log and look at the failure cause:

cpan
look LWP::Protocol::https
perl Makefile.PL
make
make test
[download]

If the output of make test (or anything earlier) is not OK, you should investigate that failure. For me, installing URI fails, for example, on a current Termux, on Android 8 (Oreo).

Update: At least the URI.pm test failure can be forced. It only happens because the test suite assumes a working /bin/pwd (which does exist but fails to work on Termux).

Update 2: After that, I need to also install openssh-dev using the Termux package manager. Net::SSLeay still fails to find the headers, but that should be fixable by setting some environment variables.

Unless you tell us more about the exact failure you get, I'll leave things be at this point in time.