Retropie performance extremely slow on 4k TV

[Rubicai]

Hi everyone I hope I can get an answer in here. I've got my first raspberry pi today, and while setting it up everything went really well. I've installed raspbian, retropie and redream (it's a raspberry pi 4 btw) and the performance was great, from cps2 to psx and dreamcast. I did that on a smaller TV, like 20" or so. After everything was set up, I moved the raspberry pi to the living room where I have my 50" 4k Sony Bravia (I add the model because I don't know if that's crucial or not). To my surprise, it's a total mess. I can live with the black borders displayed around the screen, but the texts are really small, I'd say even unreadable, and most importantly, retropie is very slow. It takes a lot of time to load the main screen and it's completely unplayable. On the other hand, redream works well, but it's set to 640x480, leaving me with a small image in the center of the screen. So well, my questions are:
1: is there any solution to the small text? Can it be resized so that it matches with the screen?
2: is there a way to get redream to display a bigger image without losing speed?
3: how can I fix retropie? Can it still be displayed to fit the entire screen and be playable?

Pd: sorry if I misspelled something, English is not my first language.

[Rubicai]

@Rubicai Okay I've finally fixed it. If someone is going through the same problem contact me and I'll tell you what worked for me.

[quicksilver]

@Rubicai there is no private message function on the forum. Any chance you could post the solution here in case others have the same issue?

[Darksavior]

The answer is to set the resolution to 1080p via raspi-config or manually through your config.txt. You're welcome.
For redream, 640x480 or 720x480 is the optimal resolution and you set that inside the emulator.

[Rubicai]

@quicksilver oh okay sorry, I was thinking maybe via email too but I'll post it

[Rubicai]

@Darksavior I had the raspberry connected in the HDMI 0 port, I changed it to the other and it's not the highest resolution but I don't really need it. I just thought both ports were the same that's why I didn't bother changing it until last minute, but thanks for replying!

[squanto]

This is how I fixed laggy N64 performance on my 4K tv:

hit F4
cd /boot
sudo vi config.txt

in config.txt, add the following to force 1080p:

hdmi_group=2
hdmi_mode=82

[hdmi:0]
hdmi_max_pixel_freq=200000000

[hdmi:1]
hdmi_max_pixel_freq=200000000