Windows

Disable Xbox Game DVR

Xbox Game DVR is known to cap FPS to 60 or even 30FPS in some cases. Disable it to resolve this issue.

Disable Fullscreen Optimizations

Source is known to be worse with fullscreen optimizations and thus you should disable it.

Open your game folder through Steam. Then, right click on hl2.exe, click Properties, go to the Compatibility tab, and then check the box that says Disable Fullscreen Optimizations.

Use High Performance power plan

Open Power Options and select the High Performance power plan, or the Ultimate Performance plan if you have Windows 10 Pro for Workstations. For AMD Ryzen users, you may have a Ryzen specific plan. Use that.

Disable Radeon Chill

Radeon Chill is a power saving feature that introduces a variable framecap. Disable it in the Radeon Settings app:

Go to the Gaming tab, then set global settings or for Team Fortress 2 only if you want to use Chill elsewhere and finally turn Chill off.

Disable Unnecessary Services

You can use the W10Privacy tool to reduce disk load and other workloads to improve performance.