Terrible idea, for all the reasons you mentioned and more.
What if you did develop a great online relationship (platonic or otherwise) with someone, and they proposed a real life meeting in the future (I mean after getting to know you and, hypothetically, the pandemic being over or contained enough that meeting would be allowed)? Would you come clean knowing they’d likely be upset you lied, or ghost them?
I used to talk to someone who lied about his age when he had no reason to. It shocked me a bit, while it didn’t end our friendship on the spot it did make me pull away from him and things fizzled out after that. It was disappointing because we’d been getting on well until then and I find making friends quite hard in the first place.
If you feel it’s slimy to say you’re only looking for friendship when you want more, you could add something like “seeking friendship with a view to a relationship” (or however you’d like to word it). That way you’re covering both bases, so to speak.
The best partners are the kind of people you’d be friends with if you weren’t dating them, anyway.