In Windows, it's possible to use SD card as RAM.
Is something similar possible in Android (with and without root)?
It's possbile. However SD Card is extremely slow, so Android don't use SD Card as a swap, using ZRAM instead
ZRAM will allocate a memory area as swap, compress unused allocated memory into this area;
ZRAM usually used on low-ram device.
However, ZRAM is battery consuming when you are in low memory situation;
If you ram is not enough, better policy is keeping as less backgourd application as possible by increasing LMK paramters;
It's possible but I would not suggest you as the SD card is way too slow to use as RAM. You can use "ROEHSOFT RAM Expander (SWAP)" app on a rooted Android device to increase RAM.