Vlc running mkv files on ipad

[Jmusich]

I have a Western Digital EX2 Ultra. From there files are deliverd to a number of devices including 2 ipads. The older is using 15.5.7 the newer 16.5.1. I have no problem runnig mp4 files on either. Running Mkv files is now not working on the older devices. To run mkv files I need to use Vlc as an assistor. Bothe devises are running the newest VLC and the access setting are identical. I get failure to connect on the older device. Am I missing something or is the reality of the matter the ipad is just too old ? It is a 2016 ipad air. Thanks