if i want quiet time i just outright say i want quiet time. i have personally not had an issue with someone getting upset about it

Absolutely. I believe having some quiet time for yourself is very important. Personally I enjoy spending time alone in peace and silence It gives me a chance to slow down, clear my thoughts and reconnect with myself. I don't think wanting some time alone means you're avoiding people sometimes you simply need a little space to recharge and find your inner peace. And I believe we should never feel bad about taking time for ourselves.

Put up a real or electronic do not disturb sign: sign on door/cubicle, change status to do not disturb in Slack, Messaging Up, WhatsApp, etc. I know when I can be interrupted or when I need no interruptions.

I insist upon it.
Whether someone else understands that or not.

Errbody needs some quiet time or else we'll get stressed and feel disturbed. Tranquility and self time allows us to reflect and build up identity, thoughts, and exert a part of our cognition that's thirsty for use

You have to have it and those around you should want it for you

It's never been difficult for me to find a time and place to be quiet so I don't really see the problem. What is the situation?