Is there any difference between "umumnya" and "biasanya"?
Can they always be used interchangeably? Thanks

'umumnya' & 'biasanya' are interchangeable in the example sentence.
I'm not sure if they are always interchangeable, because the base words have slightly different meanings.
'umum' = public, general, common.
'biasa' = usual, regular, common.

If you look up the KBBI definition of 'biasa' (see below), then you'll see that 'umum' is considered to be a synonym.

https://kbbi.web.id/biasa

biasa/bi·a·sa/ a
1 lazim; umum:
bagi masyarakat sekarang memakai sepatu sudah --;

But I'm sure that the base words are not 100% interchangeable.
For example:
'Toilet umum' (Public toilet).
'Toilet biasa' <== this doesn't work, it's not a synonym.