A Hub4 (and Hub3) has wifi5 - it will only ever achieve ~600Mbps on a single device - its just physics. It can get ~500 on two devices simultaneously - to deliver the ~1GB bandwidth.
To get higher on a single device - you must have wifi6. Note the Hub5 is wifi6 - or you can buy your own equipment.
On cable - test speeds this way...
As you expect >100Mbps then.... Connect a 1GB enabled computer/laptop (check network card is set to 1GB) , with up to date drivers, via a NEW and working Cat5e/6a ethernet cable, directly to the Hub which you have put into “modem mode” (https://www.virginmedia.com/help/virgin-media-hub-modem-mode ).
Or go into the Hub settings and turn off/disable the wifi and also disconnect all ethernet cables from the Hub. This ensures that NO other devices are connected
Test speeds at https://speedtest.samknows.com/ - or https://www.speedtest.net/ - try on 2 different browsers - as Chrome sometimes gives odd results.
If they are still low – boot your device into Windows safe+networking mode - to disable any potentially interfering software - and try again.
There are many posts on here (I have a list of ~30!) where QoS software, anti-virus, unknown/flaky software, old network card drivers, corrupted browsers, bad cables or other connected devices are limiting speeds on tests.
Report back what that gets. For examples of why... see message 7 in the first thread and 9 in in the second and 3 in the third
I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired, 1 WiFi, 1 on PA) Hub5 in modem mode with Apple Airport Extreme Router +2 Airport Express's. On 250Mbps, Talk Anytime Phone, x2 Mobile SIM only iPhones.