I was born with brown skin, but since the pandemic because i rarely go out my skin now looks white (whiter than my natural skin tone) without any treatment. is that possible? or is this a sign of disease?

No. Your skin color, if uniform, is normal. You may be vitamin D deficient due to lack of exposure to sun. Take 2000 units of vitamin D3 daily to safeguard your bone health. In case you are anemic, it would be useful to take oral iron supplement. Wish you good health!

It's difficult to tell. However, if you have a skin disease which may you lose the skin pigment, i.e. albinism, your skin won't get darker when exposing the sun so you can easily test yourself by walking in the sun for a couple hours. Moderate or severe anemia can make you look pale but not truly white but the inside of your eyelids (conjunctiva) is also pale with anemia instead of pink color.

Since you have isolated yourself for a few years and rarely go out, you may not be producing enough melanin that gives your skin it's color. You may have a condition of hypopigmentation. See a dermatologist for exam and treatment if necessary.