How else should I diversify my portfolio?

Is there a reason for that much cash? Maybe just keep 6 months of expenses as emergency funds and invest into various ETFs. ARKK is not bad, but since your allocation seems like you're quite risk adverse, maybe investing in SWRD+EIMI or VWRA would do good for you as a globally diversified core part of your portfolio.

Any reason why you're holding onto so much cash? Perhaps you're saving for a house or wedding.

But otherwise, there is a phenomenon called cash drag. It means holding too much uninvested cash in your portfolio. If you had 90% cash and 10% investment, and your investment grew by 10% - your overall wealth would only increase by 1%. That's cash drag.

On top of diversifying, consider deploying a lot more cash into investment.

Sector based investing like ARK ETFs is a good idea, but make sure that you have a solid, globally-diversified core portfolio. Growth ETFs have higher risk, so weight your portfolio accordingly. You can put more into your Stashaway / Syfe portfolios to form your core portfolio.

Beware of diversifying but not really diversifying, that is, to buy a lot of different things whose underlying holdings are the same. Make sure your Syfe and Stashaway and whatever else are invested in different securities. For example. Syfe's Equity100 has a large stake in the US market, of which Tesla is a big component. ARKK also has a large weighting towards Tesla. If you buy apples from here and buy apples from there, in the end, you just have apples. So be wary of these overweighted exposures in your portfolio.