Does reach allow a creature to block a creature with flying and landwalk at the same time?

Reach (CR 702.17) grants a creature the ability to block creatures with flying, just as if it had flying itself. So the reach ability fully handles the flying part of the blocking question — a creature with reach can block a creature that has flying.

Landwalk (CR 702.14) is a separate, independent evasion ability. A creature with landwalk (e.g., forestwalk) cannot be blocked at all if the defending player controls a land of the specified type — regardless of whether the blocking creature has reach, flying, or any other ability. Reach does nothing to overcome landwalk.

So the two abilities must be evaluated independently at the time blockers are declared (CR 509.1b). If the defending player does not control the relevant land type, the landwalk condition is not met, the attacker is blockable normally, and a creature with reach can block it despite its flying. If the defending player does control the relevant land type, the creature cannot be blocked by anything, reach or not.

Concrete example: Your opponent attacks with a 2/2 that has flying and forestwalk. You have a 1/4 Spider with reach. If you control a Forest, the 2/2 cannot be blocked at all — reach is irrelevant. If you control no Forest, you may block it with your Spider because reach covers the flying restriction.

In summary: reach solves flying, but landwalk is an entirely separate gate that reach cannot open. Whether blocking is legal depends on whether the landwalk condition (controlling the relevant land type) is currently met by the defending player.