Can you help me find a T20 Torx bit

I think you will need to get a female-female adapter  (6mm hex socket to 1/4" socket). Then your 6mm hex key can drive any 1/4" bit (including any common T20 bit).

Topeak do a T25 one.

https://www.biketart.com/products/topeak-hummer-hexus-ii-t25-bit

Not sure about T20...

T25 from Topeak I think fits a 4 mm Allen key for trailside maintenance of disk bolts etc.

https://www.sjscycles.co.uk/tools/topeak-replacement-hummer-hexus-ii-t25-bit/

Topeak don't list one on their website. Odd.

In a simlar reply to Stanley

Something like this - https://www.autodoc.co.uk/neo-tools/20451256

Would work i think, as 1/4 inch drive sits onto a 6mm allen key and works.
Its maybe a bit of a 'bodge' but it does work

Swisstool make a 1/4" to 5mm adaptor, 1/4" bring the standard drive. I have one in my Victorinox' trail tool. Wera will likely do a T20. Wera and more available from RS for one. RS unlikely to be the cheapest but when work is buying...

Swap for a hex bolt?