Two solo offerings from Crystal Cruises
Crystal Cruises have two specials on for solo cruisers. One for those that prefer ocean cruising, and the other for river cruisers.
Ocean cruisers can enjoy a reduced single supplement, as low as 125%.
More info here. https://www.crystalcruises.com/special-offers
River cruisers are far from forgotten, with 38 Deluxe window suites onboard Crystal Mozart available with NO single supplement, on all voyages from March 2022.