Firstly, I use the spelling in the primary sources.
Secondly, if there are variations, I use the commonest or most recent, and add all the sourced variants to the appropriate field, whether for Last Name At Birth or Given name.
Thirdly, I MAY put a modern, accepted spelling and mark it Uncertain if the variants are not obvious. E.g. sources only have Latinised names, such as Jana for Jane.
I use iPads and iPhones for my WT work, and they usually make good stab at what I’m trying to type. “Add to dictionary” never appears - it’s a MSWindows thing.