UK share markets have had another false start at the start of 2021. After a blistering beginning to January the new bull market ran out of steam almost as quickly as it began. The long-running Covid-19 saga rolls on and continues to play havoc with investor confidence. And it threatens to derail a solid rebound in the global economy this year.The muddy economic outlook isn’t stopping me from continuing to build my Stocks and Shares ISA, though. This is because there are still plenty of UK shares that I think could record big profits growth in 2021 regardless of the wider economic landscape. It’s also due to the fact that I invest with a view to making returns over a long-term time horizon.5G is here – and shares of this ‘sleeping giant’ could be a great way for you to potentially profit!According to one leading industry firm, the 5G boom could create a global industry worth US$12.3 TRILLION out of thin air…And if you click here we’ll show you something that could be key to unlocking 5G’s full potential…2 UK shares on my ISA radarIt’s a bonus if they can provide faster returns, of course. Here are a couple of shares I’d happily buy for my own Stocks and Shares ISA that I think could start to do well in 2021.#1: TharisaI have just explained why respondents to a London Bullion Market Association (LBMA) survey reckon silver prices will fly in 2021. The same investor concerns and macroeconomic factors (like low interest rates and a weak US dollar) that are anticipated to push the grey metal higher this year are expected to drive the prices of the platinum group metals (PGM) suite too.The LBMA reckons that average platinum and palladium prices will rise 28.2% and 11.2% respectively in 2021. This creates averages of $1,131.50 and $2,439.10 for the two chief PGMs. The precious commodities are expected to benefit from improved car making as the economic recovery kicks in. And this bodes well for UK shares like Tharisa (LSE: THS), which haul the metals out of the earth.There are significant risks to Tharisa, of course. The threat of production problems and spiralling costs are two ever-present problems for UK mining shares. Indeed, rampant Covid-19 infection rates and safety issues forced the company to shutter its operations at times in 2020. Still, in my opinion, the company’s low valuation makes it an attractive buy today. Tharisa trades on a price-to-earnings (P/E) ratio of 10 times for the fiscal year to September 2021.#2: 4Imprint GroupI believe that marketing products maker 4Imprint Group is another good UK value share for 2021. This business trades on a forward price-to-earnings growth (PEG) ratio of 0.2. Any reading below 1 suggests that a stock is being undervalued by market makers.I can understand why investors might be reluctant to pile into 4Imprint today. The prospect of a bumpy economic recovery could spell havoc for product orders at the company. But for the moment, trading continues to recover and January’s update showed its order intake improved to 70% of 2019 levels in the fourth quarter. This compares with a weekly average of 60% it recorded at the end of October. Advertising budgets recover quickly when economic conditions improve. And this could result in a blockbuster year at this UK share. Royston Wild | Sunday, 7th February, 2021 | More on: THS Click here to claim your copy now — and we’ll tell you the name of this Top US Share… free of charge! See all posts by Royston Wild Image source: Getty Images 2 cheap UK shares I’d buy in my Stocks and Shares ISA Simply click below to discover how you can take advantage of this. Royston Wild has no position in any of the shares mentioned. The Motley Fool UK has recommended 4imprint Group. Views expressed on the companies mentioned in this article are those of the writer and therefore may differ from the official recommendations we make in our subscription services such as Share Advisor, Hidden Winners and Pro. Here at The Motley Fool we believe that considering a diverse range of insights makes us better investors. Renowned stock-picker Mark Rogers and his analyst team at The Motley Fool UK have named 6 shares that they believe UK investors should consider buying NOW.So if you’re looking for more stock ideas to try and best position your portfolio today, then it might be a good day for you. Because we’re offering a full 33% off your first year of membership to our flagship share-tipping service, backed by our ‘no quibbles’ 30-day subscription fee refund guarantee. Our 6 ‘Best Buys Now’ Shares Enter Your Email Address “This Stock Could Be Like Buying Amazon in 1997” I’m sure you’ll agree that’s quite the statement from Motley Fool Co-Founder Tom Gardner.But since our US analyst team first recommended shares in this unique tech stock back in 2016, the value has soared.What’s more, we firmly believe there’s still plenty of upside in its future. In fact, even throughout the current coronavirus crisis, its performance has been beating Wall St expectations.And right now, we’re giving you a chance to discover exactly what has got our analysts all fired up about this niche industry phenomenon, in our FREE special report, A Top US Share From The Motley Fool. I would like to receive emails from you about product information and offers from The Fool and its business partners. Each of these emails will provide a link to unsubscribe from future emails. More information about how The Fool collects, stores, and handles personal data is available in its Privacy Statement.