Honestly, it depends on the material, finish, and color more than anything else. In direct sun and extreme heat, some outdoor benches absolutely get too hot to sit on—especially dark steel or iron benches. Lighter wood and quality recycled plastic benches are usually much more forgiving.
Metal benches are the worst offenders. Steel and iron hold heat, and a black or dark bronze metal bench can easily reach 140°F to 170°F on a 100°F day. That is hot enough to burn bare skin. Aluminum heats and cools faster, so it stings but doesn't stay dangerous as long. If you like the look of metal, choose a light powder-coated finish, a perforated or slatted seat, or keep it in shade.
Wood benches generally feel cooler to the touch because wood doesn't conduct heat like metal. Teak, cedar, and acacia can still get warm in full sun, but they rarely become painful the way metal does. Dark stains make them hotter, so stick with natural or light finishes if the bench will sit in the sun.
Recycled plastic or HDPE benches sit somewhere in the middle. They don't transfer heat aggressively, but dark colors still get hot. Light colors and textured finishes help. The good news is that HDPE holds up very well to UV and high heat without warping or cracking, which is why it is common in hot climates.
If you want heat-resistant bench materials for a full-sun spot, light wood and light HDPE are the safest bets. So if you're asking whether outdoor benches get too hot in extreme heat: yes, the wrong bench can. For hot, sunny spots, go with light colors, avoid solid dark metal, and think about shade. And when in doubt, do a quick tap with the back of your hand before you commit to sitting down.