I do the same, and I think it's sad that this is the best we can do in 2021 :)
(What comes to my mind, is that windows removed the option to record the audio playing directly - which means slightly advanced users can still record their songs from spotify and co, but the majority cannot)
of course security was near nonexistent, but it was home LAN, and convenience trumped all.
Nowadays I have NO idea if I could do a similar setup with Windows 10 without resorting to the cloud
Make the PC see each other in the LAN is just a matter of ticking one box. I typically create a folder somewhere and give r/w access to everyone then I proceed to log in with the credentials of the computer then put whatever I want. After I am finished I delete the folder. I think it uses SMB under the hood.
maybe running python -m http.server in Termux is more attractive.