Color Grading monitor?

How can I use one of my monitors for the color grading mini screen in Resolve?

I keep having to hit ctrl +F on the keyboard, is a pain

For grading:

https://www.blackmagicdesign.com/products/decklink

Read page 2582 of the Resolve 16.2.6 manual, "Limitations When Grading With the Viewer on a Computer Display." This explains why it's unwise to try to use a computer display for final color correction.The same problem exists with the "Clean Feed" output, since it's not color managed.

Don't try to make judgements on uncalibrated GUI displays. That will lead down a perilous road of pain and suffering. And if you do look at anything in the GUI display, don't compare it to what you see in Resolve.

The Clean Feed can be perfectly adequate if you're only editing in Resolve and don't need to make any precise color judgements on the fullscreen preview display. If you do need to see accurate color, you really need a color-managed output with a Blackmagic display device, plus a calibrated display.

The ICA has a good 1-hour video discussing different affordable options for grading displays, or at least displays that can be calibrated for Rec709.

$ wins, so even fairly big place don't use 15x Sony X300 etc., but home OLEDs

It also shows you that there is always a correlation between gear quality and project importance/level.
Not a single place will use X300 on every project as then in few months they will bankrupt.

As I don't do critical color work I don't use a managed output like a decklink card. I do, however, have both my displays calibrated. The screen with the video window on it is a used Eizo Coloredge grading display, which I got for a very good price on Ebay. The other display is a standard BenQ monitor and surprisingly is very close to the Eizo when calibrated. I've also found that I can trust what I see on the Eizo.
As to picture size I don't have the Clips or Timeline showing under the picture window so I can enlarge it for a better view.

You want to use the "Clean Feed" feature.

I got a relatively cheap 27" LG UHD computer monitor here and it is surprisingly close to a much more expensive Eizo when connected over a BM Mini Monitor and calibrated by DisplayCal with a Color Munki.
Perfect? Not at all, it has inconsistencies in backlight and some light bleeding on the sides. But much better than any uncalibrated display connected for clean feed, which in marketing claims to cover 99% Rec.709.

Edited for typo.

$ wins, so even fairly big place don't use 15x Sony X300 etc., but home OLEDs It also shows you that there is always a correlation between gear quality and project importance/level. Not a single place will use X300 on every project as then in few months they will bankrupt.

Actually, the big LA post houses do still use X300's, X310's, and some have the FSI equivalents (all approved for Dolby Vision). And then there are theatrical projectors. But I often see an LG, Panasonic, or Sony OLED off to the side as the "client display," and often that's all the client sees if they're supervising. The smart DPs will say, "let me see the 'real' monitor," and they'll check the BVM.

I have moved projects several times back and forth from our LG room to a BVM-X300 room across town, and I think we were more than 90% close in terms of picture accuracy. The BVM is $30K, the LG is $1500 (plus another $500 for calibration), so it's a good deal for what it is. But there is a very real cost of entry. I always say, "Resolve itself is cheap ($299), but it's the everything else that costs a fortune." Baselight, Nucoda, Mistika, Scratch, and Luster are all similar in that regard.

Steve Shaw of LightIllusion has a good essay on "Why Use a Grading Display?", and I think he expresses the important points very well:

https://www.lightillusion.com/grading_displays.html

Of course they have reference screens but use them about only for projects which can pay for it.
Once you pass some level of accuracy it’s meaningless anyway as not a screen wins an Oscar, but people for their talent and skills.

Many even cheaper screens will calibrate well for Rec.709. It’s now more important to have screen with good black/contrast levels, uniformity and angles. Colour deltas are probably not the biggest problem at all.

The only reason why clean feed to a computer monitor would be inaccurate is that it lacks 10-bit support in Windows (cannot comment whether Professional GPUs do since I don't own one) so you really can't judge if eventual banding is in the timeline or in the monitor. Also, monitors are not TVs and may not sync to timeline fps settings but that's beyond the point since we talk color accuracy.

All of this is true for Resolve.
There are apps which will do all mentioned and provide accurate preview. Need of dedicated “preview card” as a hardware is fading.

My sony 65 inch smart tv looks different when watching things like you tube videos than when i watch on my computer.
What about a 32 inch smart tv for an external color grading/editing monitor with the deck link? since a tv is more likely for watching movies...