At the start of 2026, I hold 24 different businesses in my Stocks and Shares ISA. But the largest position by a significant margin right now is Shopify (NASDAQ:SHOP) – not because I’ve invested the most in this business, but because it’s been a stellar performer.

Since I first bought its shares back in September 2017, the e-commerce fintech platform has expanded its market-cap by just shy of 2,700% – and that’s even after crashing by 85% a few years ago.

While the volatility in 2022 was certainly unpleasant, the underlying company and its long-term potential remained perfectly intact. So while everyone else was selling, I was busy buying. And those more recent investments have also generated superb returns ranging 220%-360% over roughly the last three years.

Needless to say, Shopify’s been a huge money-maker and market-beater for my ISA. But the question now is, can it do it all again?

More untapped growth potential

With a market-cap now sitting close to $214bn, I’m not expecting another 2,700% surge anytime soon. Even a 300% boost would be quite a challenging feat since it would require Shopify to grow to a roughly $850bn enterprise.

However, that doesn’t mean to say it still can’t deliver robust wealth-building gains that outpace the US stock market’s 10% annualised average return.

The bulk of the company’s cash flow stems from charging small transaction fees from each purchase made through a Shopify-powered website. In the US, that’s roughly 30% of all online stores today. But internationally, that figure drops to around 10%, revealing plenty of long-term growth potential.

Combine that with free cash flow margins sitting in double-digit territory even after scaling operations rapidly, and the business is a self-sustaining, cash-generating machine.

What’s more, that cash is most recently being put to work delivering new AI tools to help merchants reduce sales friction and improve customer experience – a technological advantage that many of its rivals are struggling to replicate.

There are always risks

Despite my bullish outlook, even I have to admit Shopify’s valuation is definitely getting a bit stretched at a forward price-to-earnings ratio of 88.5. In fact, this extreme valuation, combined with its dominance in my Stocks and Shares ISA, is why I’ve actually been trimming down my position.

The vast gloomy predictions of a US recession prove accurate, its core customer base could suffer a rapid decline in shopping activity, directly impacting Shopify’s all-important transaction fee revenue stream.

But the damage could spread even further. While a smaller part of the business, Shopify’s Buy Now Pay Later credits losses could expand as consumers fail to keep up with payments in a tough recessionary environment.

The group’s financial strength means Shopify’s well prepared for a cyclical downturn. But at such a lofty valuation, it seems the market isn’t. And if the worse does come to pass, Shopify’s share price could see yet another 2022-style pullback.

Bottom line: while I’m still bullish and intent on holding my shares, I think there are far better and more reasonably-priced growth opportunities for investors to consider for their Stocks and Shares ISAs today.