I think what my secondary platform was has shifted quite a bit over the close-to-thirty years I've been playing video games, so I'll try to make a timeline:
1995 to 2005: PC primary, Nintendo 64 and later GameCube secondary
Got into gaming when I was around 7, 8 years old. My parents had a laptop with a disc drive that I could play games on, later I got a Nintendo 64 from my communion money and was given my own PC when I entered high school. Console gaming was strictly limited - first an hour a day, then only on Saturday mornings "after I did my chores" (so basically two hours per week unless my dad wanted to watch some race, then it was more-or-less cancelled), meaning the PC was the system I could play on freely.
2005 to 2009: PS2 and GBA primary, GameCube/Wii secondary, PC tertiary until 2007
Got a PS2 for my 18th birthday and around the same time, I had purchased a new monitor with SCART and Component inputs, so I had more freedom to play console games. Around the same time, I got into handheld gaming via the GBA which kinda became my other main system for quite a while. Started falling off of PC gaming outside of some older titles and the OG Guild Wars and in 2007 I sold my PC to purchase a MacBook.
2009 to 2013: PSP and DS primary, PSWii60 secondary
Yes, I owned all three home consoles (the first and only generation where this had ever happened), but since I was at my dorm room at uni a lot during this period, these systems fell by the wayside and I even went so far as to sell my Xbox360 (which I kinda regret nowadays) and kept only the Wii and the PS3 (which still serves as my BD player).
2013 to 2017: 3DS primary, PC and Vita secondary
I started getting back into PC gaming in about 2013, when Valve's Steam became available on MacOS. After a while, I wanted to explore gaming on Windows again and started using a laptop for that purpose while the MacBook was relegated to being an uni device. Like the years prior, I focussed on handhelds, but the 3DS got more attention from me than the Vita by a wide margin. Also, I thought all the home consoles from Gen 8 sucked. Oh wait. I still think that.
2017 to now: Switch primary, PC secondary
For my 30th Birthday, I bought a Switch with Breath of the Wild and it has been my main gaming device ever since. For pretty much everything else, I have a PC and while I do use Steam, I don't use it exclusively any more and purchase my games at other services and even key sites. I also went and fulfilled a long-time dream of building my own PC.
Future prediction: Switch 2 and PC primary, PS5 secondary.
At this point, I'm considering buying a PS5 mainly for the purpose of having a 4K BD player. With the rise of handheld PCs, I think I might take a dip into that particular territory, as it suits my gaming interests well. And yes, buying a Switch 2 or whatever is very much a lock-in if Nintendo stays with the hybrid form factor.