Welcome and all the best
I use both IBKR & Swissquote. Mainly for diversification of brokerage purposes. And also I somehow wanted a Swiss broker too where I can knock on their doors if I really had to.
All this is very personal and maybe doesn’t apply for everyone. For me investing is not only about optimisation of costs , it’s also about optimisation of personal peace of mind. Just try to find balance.
I diversify everything -: Brokerages, Fund houses, ETF domiciles, Banks 
I also started with IBKR only but then later added SQ to my mix. I buy UCITS ETFs on SQ though.
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It’s good that you are thinking about international diversification. I recommend you to watch the videos from Ben felix about this
But remember you are already using VT which has exposure to all countries. So if you don’t have specific focus on Europe or CH or Emerging, then you can just use VT or any other world ETF.
However if you want specific exposure to regions, JUSTETF is a good website to sort through major ETFs. Some of my favourite ones are following. But there are many to choose from.
- EIMI for Emerging markets
- VEUR for Europe
- FLXI for India