This app was mentioned in 9 comments, with an average of 2.89 upvotes
Dream House Days on mobile.
Dream House Days on mobile.
Dream House Days on mobile.
Hmm, I can only think about Visual Novels for the Switch, but most of them follow a genre, such as Mystery, detective, etc..
As many have have suggested, it seems life simulators are the closest you can get to a Hallmark feel, and I can't think of anything other than The Sims series. Sadly, EA and Nintendo are not friendly, so hoping for the sims to make it to the Switch seems far from reach, but that doesn't mean, we can't hope for it to happen. Maybe you can play The Sims on mobage? Some other titles on mobage that have a "sims" feel that I can think of Are Virtual Villagers. (iOS version for free)
Another title that I've been suggesting a lot was Spiritfarer. Although it's not about romance, but it's about helping your spirit friends (who are ghosts) to accomplish the very last thing they want to do while they were alive, but wasn't able to accomplish their goal before they embark on their journey to the afterlife. It's very wholesome, and heartwarming, and it made me appreciate life a lot. Trailer
To The Moon is sort of similar to Spiritfarer, but it's very wholesome as you play as a pair of doctors to accomplish a dying man's memories to accomplish his goals. Trailer
Florence seems something more like Hallmark. Although it's very short game, I did enjoy it on my mobile device. Trailer
Dream House Days DX (free to play on mobage! iOS | Android) You play as an architect and landlord to build a town of your own. Tenants can come to you for advice about romance, and career. Kairosoft has a lot of titles, mostly management and simulation for businesses. Some of them like Dream Town Story (I don't remember if that's the one I played) will give you a chance to romance some of the tenants that move into your town, and best of all, seasons do change throughout the game.
It's not a lot to list, but I hope some of these caught your eye. :]
It's Dream House Days. Looks interesting, as you build houses, add furniture and rent them.