TinkerCAD

Hi all, I have big problem with Tinkercad since two weeks now... Suddenly (like from one day to the other) the reaction when moving or manipulating parts of a design, or even only shifting view angle with mouse moves is dead slow! It is almost impossible to use now for me. I have decent internet speed (true 32MBit/s), my computer is not the newest but worked fine with Tinkercad until the last weeks. When I use my wifes laptop everything is ok.
I tried 3 different browsers on my computer without any improvements, its equally slow with each browser.
I also checked Plug-ins, security settings and tried out almost everything without any advance.
Glad to get some input here!
Thanks,
BR
Nick

Okay, I needto carefully think about my words since I'm Dutch and Tinkercad somehow automatically appears to me in my own language. I don't wish that because it makes communicating with other peole all over the world rather difficult. But anyway, I still hope that you guys will somehow what I'm trying to explain here without me knowing the exact English words used in the program.
I'm designing a miniature lamp as you can see in the pictures. It's about 6 cm in diameter so not the world biggest object.
The lamp itself slows things very down, I build it with ctr-D and contains 16 sections that I could easily group together.
I then wanted to remove the bottom and add an extra edge.
From there the design no longer loads properly. It's like the lamp doesn't 'accept' transparent circle. It keeps loading and loading but it never gets where I want it to be.
Closing the page and starting it again doesn't help either.
So I was wondering: how many 'vectors' can Tinkercad handle at the same time?
And what should I be able to do about it?

Thanks in advance.

For some reason this doesn't appear on my designs page: https://www.thingiverse.com/thing:4645609

https://www.thingiverse.com/garble/designs

I thought maybe I did something to make it invisible? Earlier submissions appeared for me even when they were just unpublished drafts.

Is it possible to upload my own shape/object to the shapes menu? Would love to have my own commonly used shapes in the menu of every design.

Greetings,
I need a little design help, I printed these Lithophanes (https://www.thingiverse.com/thing:3154700),using one of the Tarman files for size reference, and modified this two sided frame (https://www.thingiverse.com/thing:2770308) for Halloween. I would like to create a blank backplate that will fit in the frame, but cannot figure out how to do it.
Added a pic for reference.

TIA