I am having what appears to be the same problem as the OP. In 2/3 different saves which seem pretty early game (just after opening the laundromat), a bug is occurring that causes the fps to drop to single digits.

I had not noticed the item issue at first but I had the same exact problem in at least one of these instances:
"worker gets stuck at the detergent shelf and will not move to serve customers, pickup deliveries, etc. Detergent item gets left behind when issue resolved. Single digit fps persists whenever camera is near laundromat and camera is moving"

At first I just started a new save due to the fps being unplayable. In my second attempt the bug happened while I was not looking at the laundromat. I checked on the laundromat and found that all my employees had disappeared, workers, engineers, cleaners, all of them were showing 0 employees, a couple detergents remained on the floor, and the <10fps again was happening.

I kept playing the second save and noticed that the fps only drops when the camera is moving and is near the laundromat at a zoomed in level. If I zoom all the way out, fps returns to normal (75-100). If I move the camera away from the laundromat, fps is normal. If I bring the laundromat in the cameras view, zoomed in, and leave the camera still: fps is low but not single digit. Unfortunately my fps ticker isnt showing in the screenshots.

dxdiag [file.io]
screenshots [file.io]

With the item topic in mind, I revisited both of those saves and found that there is one detergent in each with similar behavior and characteristics. As long as this item is on-screen or just off screen but near the edge, the fps issue occurs. I can look at half of the laundromat and have the fps be just fine if this item is not displayed.

On both saves there is a detergent which was left behind at or around the time the issue started. This item has no information on its mouse-over tool-tip other than 'Detergent'. I am somewhat more confident that this detergent is related to or the cause of the fps issue.

screenshots [file.io]
video

Turning off product qualities overlay seems to fix this issue entirely as long as this overlay remains 'off'. Fps issue returns if product quality overlay is re-enabled.

What you descriped was exectly my issue. But i didnt tried to turn of the overlay. I already started a new game

Once I unlocked the chicken shop, i had a similar issue there and now the fps problem persists everywhere. Anytime I open the product quality overlay, I have 1fps regardless of where the camera is on the map.