This set contains four of the five Sovereign denominations (minus the five-sovereign piece) issued in 2021. All coins feature the special crown privy mark to celebrate the 95th birthday of Queen Elizabeth II.
The Royal Mint says about the set:
"From its royal beginnings to today, The Sovereign has always been closely associated with the monarch. Over Her Majesty The Queen’s long reign, The Sovereign has marked many milestones, from jubilees to birthdays and anniversaries. For 2021, the four coins in this set feature a unique ‘95’ crown privy mark, which will appear for this year only. The Sovereign coin itself also has a milled edge, which features a symbolic 95 mills in celebration of The Queen’s 95th birthday."