Short Answer: No.
Long Answer: The Switch CPU architecture is aarch64 and unless some support is brought for other architectures by those companies to their apps you won't be able to run Steam and other x86_64 apps natively. However, box64 is available for Switch and allows for x86_64 to arm64 emulation. box86 is also available for x86 to armhf but lacks proper GPU acceleration since Nvidia does not provide armhf GPU drivers. Fex is also in development for Switch, which allows emulation of x86_64 and x86 applications.
Many console emulators are open sourced and/or have native support for aarch64. Projects such as RetroArch (including a Lakka RetroArch Linux Distro) and RetroPie (under L4T Ubuntu Bionic) have native support.
With your Switch connected to your PC with a USB C -> A Cable:
Tools -> USB Tools -> USB Mass Storage > SD Card
Within Linux (network share):
Setup SMB/Samba sharing on Windows or Linux (many right ways to do so)
Mount the share in Linux on Switch (cifs-utils or gigolo)
Within Android (usb or network share):
Download an FTP server from Google Play (requires Gapps) or plug in to a computer and select File Transfer from the USB options dropdown
No. Currently L4T / Android don't have support for the newer, Mariko-based models. Adding support would require extensive bootstack and kernel modifications. We have finished raising money for Mariko (Switch v2, Lite, OLED) dev hardware so we can add Linux and Android support to these devices, and work is in progress.