Lineage14120180419unofficialgtel3g: __link__

Yes, the "gtel3g" designation specifically implies support for the SM-T561's cellular data and voice capabilities, unlike the "gtelwifi" (SM-T560) version.

Virtually zero. Most basic apps require Android 5.0+ or 7.0+. lineage14120180419unofficialgtel3g

Power off the tablet, then hold Volume Up + Home + Power to enter TWRP. lineage14120180419unofficialgtel3g