At least for Linux (and some *BSD) based OS distributions, https://www.distrowatch.com/ lists versions of major included packages (including perl). If there is a particular distribution in use at the client location, then this might be of help.
For the top 21 distributions viewed on their site in the past six (6) months, the perl version breakdown for the last two (2) (or so) releases is as follows:
- 5.14.1 (Arch 2011.08.19)
- 5.16.3 (CentOS 7.8.2003)
- 5.22.1 (Zorin OS 12.4)
- 5.24.1 (deepin 15.11, MX Linux 18.3)
- 5.26.1 (elementary OS 5.1.7 (hera), elementary OS 5.0 (juno), Linuxfx 9.4, OpenSUSE 15.2, Puppy 9.0 (bionicpup), Zorin OS 15.3)
- 5.26.3 (CentOS 8.2.2004)
- 5.28.1 (antiX 19.3, Debian 10 (buster), deepin 20.1, Linux Mint 4-LMDE (debbie), MX Linux 19.3, Solus 4.0)
- 5.30.0 (Kali 2019.4, KDE Neon 20210114, KDE Neon 20201231, Linuxfx 10.7.105, Linux Mint 20.1 (ulyana), Pop!_OS 20.04, Puppy 9.5 (fossapup), Ubuntu 20.04 LTS (focal), Ubuntu kylin 20.04 (focal))
- 5.30.1 (Endeavour 2019.12.22, Solus 4.1)
- 5.30.2 (Fedora 32)
- 5.30.3 (Kali 2020.4, Pop!_OS 20.10, Ubuntu 20.10 (groovy), Ubuntu Kylin 20.10 (groovy))
- 5.32.0 (antiX bullseye-alpha1, Arch current, Debian unstable (sid), Debian testing (bullseye), Endeavour 2020.09.20, Fedora rawhide, Fedora 33, Manjaro stable, Manjaro 20.2.1, OpenSUSE tumbleweed, Ubuntu snapshot (hirsute))
Hope that helps.