InDesign becoming sluggish with bigger text frames

[J van E]

I have a BRAND NEW iMac (OS X 10.15.7) and use InDesign 15.1.3 on it. On my previous iMac InDesign ran flawlessly but on my new iMac InDesign becomes sluggish whenever text frames get bigger or longer... For instance, when I put the cursor at the top of a text and start selecting it using 'Shift-Command-arrow down' and press that 6 times it takes a while before the text is actually being selected. Also when I want to move the cursor down (without selecting) it takes a while before the cursor arrives where I want it (and due to this I often overshoot my 'destination' because of this).

The odd thing is that I noticed that the longer or bigger the text frame gets, the slower things become. So if I have a small frame with just 4 paragraphs the cursor moves quite alright but if I make that frame longer without adding text (so just more empty space at the bottom) the cursor becomes sluggish!

Anyone knows what might be causing this? I expected my brand new iMac to perform BETTER instead of worse in InDesign!

[J van E · Accepted solution]

Never mind, found the solution: I needed to turn on GPU-performance in the preferences. Never needed that on my old iMac.