Immediately onto the lap.

SSH over Tailscale to Termux (all three free) using private-key authentication — two levels of e2ee, and fairly easy to use.

For small bits of text, I use one of these, depending on the direction and the source device:

• Laptop → phone: xclip -o | ssh phone termux-clipboard-set
• Laptop ← phone: ssh phone termux-clipboard-get | xclip
• Phone → laptop: termux-clipboard-get | ssh laptop DISPLAY=:0 xclip
• Phone ← laptop: ssh laptop DISPLAY=:0 xclip -o | termux-clipboard-set

For larger things, or files, I use scp. For other devices that I haven’t setup beforehand, or can’t set up (e.g. can’t run arbitrary programs), I connect to my phone’s hotspot, and use Total Commander’s Wi-Fi transfer addon for files (both of which are also free). Small strings I just copy over by eye and hope it goes well.