Learn Spanish (Latin America): Que yo sepa, este lienzo es viejo.

Que yo sepa is a fixed phrase meaning "as far as I know" or "to my knowledge." It uses the subjunctive because it expresses a limitation on what you know—you are implicitly admitting there is room for doubt and that your knowledge might be incomplete.

Does lienzo just mean "canvas"?

Literally, it means "canvas" or "linen." In art contexts, it refers to the physical material a painting is made on, and by extension, it is frequently used to refer to the painting itself.

Why is it es viejo instead of está viejo?

We use ser (es viejo) when stating an objective, defining characteristic of the item, such as its factual age. You could use estar (está viejo) if you wanted to emphasize a physical change in state—for example, that the canvas looks visibly worn out, fragile, or deteriorated compared to how it used to be.

I always mix up este and esto. Why is it este lienzo here?

Este is a demonstrative adjective used right before a masculine singular noun like lienzo. Esto is a neuter pronoun used for abstract concepts, general situations, or unidentified objects, and it is never placed directly in front of a noun.