% uname -a
FreeBSD FreeBSD 12.1-RELEASE-p8 FreeBSD 12.1-RELEASE-p8 GENERIC amd64
I have installed less from ports:
% /usr/local/bin/less --version
less 551 (PCRE regular expressions)
Launching less with the "--mouse" option prevents selecting and copying text in xterm compliant terminals by the usual left-down-clicking.
How to replicate:
1) Install less from ports
2) /usr/local/bin/less /var/log/messages.
Select a block of text by left-down-clicking: this work
3) /usr/local/bin/less --mouse /var/log/messages
Select a block of text by left-down-clicking: doesn't work.
Workaround: selecting a block of text by [SHIFT] + left-down-clicking: works, but it is not expected behaviour.
Same thing happens if $PAGER is set to "/usr/local/bin/less --mouse".
LESS=-i -m +Gg
Resetting $LESS to null doesn't solve the issue.
Upstream issue was reported 14th of Feb 2020.
The workaround suggested here is to hold down shift while selecting.
No comment upstream as to whether this was the intended behaviour or not, nor any pull requests to address it.