Distance is pretty unimportant, it's all about infrastructure, here's my experience with it.

I lived in San Jose for 4 months, bussing was impossible so I biked. About a 1hr ride each way accross 12km. The middle third was by an airport in a dedicated bike route, it was a breeze, about a third was in side streets with "share the road" bullshit, it wasn't particularly dangerous but I had to hard brake quite often which made it the most tiring part of the ride. The last third was on busy stroads in bike gutters, this was almost unbearable. Broken glass from accidents was not cleaned off the bike lane so I got flats extremely frequently (10+ a month). There was a full piece of windshield taking up the whole lane for 3weeks. often cars would come dangerously close to me, and on a few occasions I got clipped by their mirrors (they never stopped), about half way through my stay a millionaire was successful in lobbying to remove the bike lane on part of my ride which made it even more dangerous. Besides the commute itself there were other problems. My work had a dedicated bike lockup, but my apartment did not, which lead to me first bike rusting through (partially my own fault for buying the cheapest bike I could find) and my second bike getting stolen. Overall it would have been cheaper to Uber every day (this was back in 2016 when Uber was very cheap) although it was a nice way to get in shape. I was more or less exhausted when I got in, both mentally and physically, and needed to shower and change clothes. 1/10 practically suicide.

I also biked in markham ontario during covid so as to avoid taking the bus. This was 30 min one way, about the same time as taking the bus, 5km journey. It involved biking down highway 7. It was safer than the stroud in Cali by a significant margin since it had bike lanes with cones separating them. It was still a highway however with cars and trucks passing me going 80kph. Trucks were the biggest problem since the grit and smoke from them would hit me right in the face, I would worry about my long term lung health. There was a single 100m stretch that was extremely scary, first there was construction under a bridge (that had been going on for 4 years) where the bike lane just ended, the bus lane also changed from 2 to 1 lane at the same time which meant all the drivers were very confused and distracted. Immediately after the underpass was an on ramp to a highway, my protected bike lane turned into a bike gutter and cars would have to cross my lane to get to the onramp. I would pretty consistently have to hard emergency brake to avoid cars that didn't see me, or cars seeing me and doing stupid shit like slowing down to 30 to pass behind me. The bike lanes were also not cleared in winter. I was usually not too tired when getting home, but mentally a little on edge. If I wasn't in a hurry I could get away without needing to shower or change at work. 4/10 doable long term but unpleasant.

Now I live in a bikable city, and although I wfh I use my bike as my primary transport. I have not had a single dangerous interaction, I have protected concrete barrier bike lanes to most of the places I want to go, with a very well maintained bike trail for the middle of town. The experience is night and day, I go faster, more directly and with less fatigue. I routinely go 20km or more in 30min and I always feel less tired than on either of my previous commutes. 10/10 both enjoyable and functional.

I would recommend walking through your route with Google street view, doing a dry run before you commit if you can, and actually get a feel for what conditions are like on your route, paying special attention for any time you have to share the road, any time cars change lanes through the bike lanes and the number of red lights. If you get snow ow would also try to get an idea of how quickly bike lanes are cleared if at all. I'll also note that an ebike can make traffic lights and hills much less frustrating. Invest in bike insurance unless you have somewhere enclosed to lockup in (some lock brands offer passable insurance).