Finally managed the transition from Prestashop to ThirtyBees. Took my time and made it more difficult by trying to bring over my entire Customer history. Used a module [MigrationPro] and then several table copies for the stuff they don't bring over.
Went live with ThirtyBees 1.4.0/PHP 8 so hopefully freed from the problem of my ISP moving PHP along faster than I'd like.
I've just discovered Thirtybees and from what I've seen so far, they are much better than zen cart, which I've enjoyed using but they've still got unfriendly urls unless you add a plugin - I'm preparing to migrate to thirtybees as soon as I've sussed it all out! Thanks @thirtybees