I've positions worth 100K in Saxo. I should have researched better as I realise that I'm loosing money on custody fees and exchange rate. Is it better to switch to IB? Will I have to sell positions?

Saxo charges 50 EUR per ISIN for outgoing position transfers, capped at 160 EUR per transfer request. This means that if you transfer everything at once, you will be charged a maximum of 160 EUR, which will definitely be cheaper than liquidating your positions. Interactive Brokers does not charge for incoming position transfers.

If your positions are worth over 100K USD, it will definitely be better to switch to Interactive Brokers, as their commissions and fees are much lower compared to Saxo, especially for foreign currency exchange transactions. The minimum 10 USD monthly minimum commission will be waived as well as long as your account value is over 100K USD.

I suggest opening an account with Interactive Brokers first. Once your account is opened, you will obtain an account number that you can use to initiate transfers. You may have to submit requests on both sides in order to transfer your positions.

I believe IB allows transfer in of holdings from other brokers. Saw it on their website sometime ago.