This ideas pops up pretty often, and people have their opinions. Personally, I suggest against this, especially if you are older (40+ years).
I’ve tried this, and it is a hindrance to some of the critical apps I use regularly, such as Camera, Maps, Messages, and occasionally the Phone App.[1] Of course, you can set shortcuts in the Control Center, double-tap the back of your phone, and all of that jazz, but it is slower, and the UX is a hindrance when you need it.
Instead, have the minimal App on your HomeScreen to avoid distractions as much as possible and/or remove the usual suspects — Social Media Apps, Games, etc. The idea is to make your Phone boring but just works when you need it. You can continue to use them on your desktop/laptop, which prevents that easy reach when you are not at your desk. Read[2] or write[3] if you are serious about avoiding distractions. If you already use a Smartwatch,[4] you can reduce your phone usage a lot more.
And the eyes work much harder in the Grayscale than in well-contrast colors. I prefer most things minimal; no labels, no text where not needed, learn shortcuts, etc. However, my phone is set to show labels and has higher contrast in the evening/night, while it shows no labels during the day. If I have to glance at it at night while driving or wake up to VIP/critical calls at night, I can see way faster and easier than squinting my eyes or fumbling for the glass. Grayscale is horribly in this situation.
And shooting photos in Grayscale, even if the actual photos are in color, is another blunder. I want to see the shades while shooting to compensate for any errors. Again, especially in the dark (however good phone AIs have become), it will always be either too bright and saturated (compensated by the AI) or too dark with a chance in lens at the last moment, trying to focus elsewhere.
1. https://brajeshwar.com/2024/phone/
2. https://brajeshwar.com/books/
3. https://brajeshwar.com/2025/notes/
4. https://brajeshwar.com/2024/watch-tiny-handy-computer/