Frame rate Windows 10 Youtube video

Since i updated to Windows 10 YouTube, Rumble, and X videos will not play at a normal frame rate in full screen mode on my 4K Monitor.

When i do not set to full screen mode the videos play at a much higher frame rate (but not normal), at full screen the frame rate appears to be about 3/second.
DVDs played with PowerDVD appear to play at the normal frame rate in full screen mode. i was thinking i needed to upgrade my graphics card, since it is so old, until i discovered DVDs appear to play properly.

i do not use this system to play games, mostly i read the news and watch YouTube music videos.

When i had Centurylink DSL and Windows 7 i could watch YouTube videos in full screen mode at 710 and sometimes 1080.

i did search the forums for similar issues, but didn't find any that pertain. That doesn't mean there aren't any, probably i just did not discover the exact search terms.

i have StarLink.
Windows 10 Pro version 22H2
Samsung U32J59x
XFX FX777AZNF4 HD 7770 Core Edition 1000MHz 1 GB DDR5
ASUS 970 Pro Gaming/Aura ATX DDR3 AM3 Motherboard
AMD CPU HDZ955FBGMBOX Phenom II X4 955 Black Edition 3.2GHz
Corsair CML16GX3M2A1600C9 Vengeance 16GB (2 x 8GB) DDR3 1600 MHz (PC3 12800)

This issue started after i installed Windows 10, while i still had CenturyLink DSL, which, on a good day, could get up to 6 mbps.

Ookla Speedtest shows 21 ms ping, 96 to 130 mbps download, and 11 to 27 mbps upload, all with Vivaldi and other programs running.

i also have an LG 4K smart tv, YouTube videos in full screen mode appear to operate properly through the wireless StarLink connection.

i use the Vivaldi browser on my PC.

Before i installed Windows 10, i was able to play Blu-ray movies from my internal LG Blu-ray disc drive using Leawo. i have not tried this after the Windows 10 installation.

Windows indicates the graphics card drivers are up to date. AMD does not have any driver downloads for HD7770.

i have YouTube Premium, i downloaded a video. It exhibits the same issue, is this what you asked for?

Many searches with DuckDuckGo and Google have not returned any useful results.

i just tried using Chrome, same issue.

The pc was connected through HDMI port 2, but freesync was turned off. Turning it on made no difference,
The monitor information (in the menu) indicates 30 Hz on both HDMI 1 and HDMI 2.
The graphics card does have a Display Port connection.

None of this explains why the YouTube, X, and Rumble video performance was ok with Windows 7 and is bad with Windows 10.

You think it's worth getting a Display Port cable to see if it makes a difference?

BTW, i am also using Malwarebytes VPN.