I wouldn't imagine it would be possible to side-load apps on a box like that easily, unless there is some sort of custom firmware available for it. I've only got experience of a Humax Freeview PVR though, so hopefully a current or ex-BT/Humax YouView box owner can advise. Due to the age of the box, I would suspect your app/vpn needs are more
Download Humax HDR Fox-T2 Digital Recorder Custom Firmware 1.03.12_mod/3.03 - Firmware
Over the past few years, Humax has been the king of the set-top-box, be it Freeview, Freesat, standard or high definition. Part of the appeal is that Humax products are very approachable – and we include the Fox T2 in this category. The supplied remote is simple, yet very effective. The clearly labelled buttons are given space to breathe
Humax Foxsat-hdr, Humax HDR1000S, 2x HDR-FOX T2, Sony STRDN1050 receiver, Sony KDL-40W4000 TV. Ether try asking the box to manual check for a software update.
FYI re my "downgrading / upgrading" comments the HUMAX support team sent me{"I'm sorry to hear that you're experiencing difficulties with your box. It would indeed seem like there is a problem with the hard-drive and the best option to resolve this requires you to firstly downgrade the software, carry out a format and to then update the software"
Download Humax HDR Fox-T2 Digital Recorder Custom Firmware 1.02.20_mod/3.10 - Firmware
mzS9. 83 183 649 428 918 127 793 769
humax nano t2 firmware update