I'm using GT1 too. Noticed a few issues:

1) Watching online streaming movies (eg. Using Exodus) sometimes can be choppy. I'm using wired LAN and using Time 100Mbps. Shouldn't be bandwidth issue.

2) H.265 files are soft and fuzzy in Kodi. Like very bad antialiasing. Other format seems ok. Video quality with Kodi 16.1 with amcodec is much better, but whenever amcodec is selected, kodi keep crashing. Upgraded Kodi to v17. No more amcodec. So video quality for h.265 becomes bad.

3) Initially I didn't notice my GT1 has dark scene problem until I played some really dark scene movies, the picture was dark and can't see much details. Read in beelink forum that a temporary workaround is to play any 4k video first, then try play back the dark scene video again. It becomes brighter.

4) Touch wood. So far I didn't experience any green screen issue. I guess that depends on TV and HDMI port.

I have updated the firmware to the latest version (104_MO) via OTA. What firmware version are you on now?