I can confirm that the RX100VA can accept a USB interovolometer. I bought the one below off Amazon and I can use it with both my 100VA and A7iii.

I have not tried using the Sony Imaging Edge app yet.

Neewer DSLR Camera Shutter... https://www.amazon.com/dp/B00NSE1F6I?ref=ppx_pop_mob_ap_share

I have a shutter release from neweer for Sony cameras. It works as expected with an a7iii. It does not work at all with an a9, but there's no apparent reason why it shouldn't. Any ideas?