You can mount a 75 inch TV on a 70 inch mount as long as the mount has the correct size VESA mount. The VESA mount is a standardized pattern of mounting holes on the back of your TV, and it determines the compatibility between the TV and the mount.
Most mounts are marketed up to 70 inches because that was the largest size that was widely affordable for a while. However, with advancements in technology, TVs have become thinner and lighter, even at larger sizes. A 75 inch TV today probably weighs what a 55 inch TV did from 6-7 years ago. So, even though the mount may be marketed for up to 70 inches, it should still be able to support a 75 inch TV if it has the correct VESA mount.
To ensure compatibility, you need to check the VESA mount specifications of both your TV and the mount. The VESA mount specification refers to the distance between the mounting holes on the back of the TV in millimeters. For example, a VESA mount specification of 400×400 means that the mounting holes are 400mm apart horizontally and vertically.
When selecting a mount, make sure it has the same VESA mount size as your TV or a larger one. For a 75 inch TV, the VESA mount size is typically 400×400 or larger. If your mount has a smaller VESA mount size, it may not be compatible with your TV. However, if the mount has a larger VESA mount size, you can still use it by using spacers or an adapter plate to fit the mounting holes on your TV.
Mounting the TV on studs is generally recommended for the best stability and support. However, if you are unable to mount directly into studs, there are alternatives. There are heavy-duty drywall anchors available that can support a significant amount of weight. Look for anchors that are rated for at least 50 pounds per anchor point. Be sure to follow the manufacturer’s instructions for proper installation.
As long as the VESA mount size is compatible and the mount is securely installed, you can mount a 75 inch TV on a 70 inch mount. Just ensure that the mount has the necessary weight capacity to support your TV.