Can you tell me which card can fit in it. I really want Nvidia card that can play Microsoft Flight Simulator at medium or high. my budget is $150.

7010 cpu (3rd gen Intel cpu) is on the weak side for Microsoft flight stimulator.  To play at medium to high setting you probably need a faster pc, or move DT components into a mini tower case so you can upgrade psu to support a fast gpu.  A very fast gpu may compensate a bit of slow cpu you have, although gpu will still be bottlenecked by slow cpu.

Microsoft Flight Simulator 2020 Requirements: Minimum configuration to play the game 

• CPU: Intel Core i5-4460 or AMD Ryzen 3 1200
• RAM: 8 GB
• OS: Windows 10 64-bit
• VIDEO CARD: Radeon RX 570 or GeForce GTX 770 
• PIXEL SHADER: 5.0
• VERTEX SHADER: 5.0
• FREE DISK SPACE: 150 GB
• DEDICATED VIDEO RAM: 2048 MB

Microsoft Flight Simulator 2020 Requirements: Recommended configuration to play the game 

• CPU: Intel Core i5-8400 or AMD Ryzen 5 1500X or better
• RAM: 16 GB
• OS: Windows 10 64-bit
• VIDEO CARD: Radeon RX 590 or GeForce GTX 970
• PIXEL SHADER: 5.1
• VERTEX SHADER: 5.1
• FREE DISK SPACE: 150 GB
• DEDICATED VIDEO RAM: 4096 MB

It is a microATX motherboard.  a minitower or full tower case will do.  user posted pinout of motherboard 5-pin power switch.

you may lose front panel usb/audio of board in new case because of Dell proprietary front IO pinout that is difficult to map out to new case.

Another way to use a faster GPU, if you don't mind it sitting outside the case - PCI-e x16 extender riser cable:  https://www.amazon.com/s?k=pci-e+x16+extender&ref=nb_sb_noss  Link shows a few.

https://m.youtube.com/results?search_query=Pci-e+x16+extender 

@CoolBoyPreston 's other post:  https://www.dell.com/community/Optiplex-Desktops/Dell-optiplex-7010-DT-GPU-upgrade/m-p/7807874#M48567 

thanks guys I am gonna buy a new case. then I'll buy a new gpu.

Since this is the thread that mentioned Flight Simulator, I'm pasting this here from @CoolBoyPreston 's other thread:

I'm also noting going back to Flight Simulator's minimum and recommended system requirements (I wouldn't as sure or as confident about minimum), you may want to consider upgrading systems entirely.  Might be much easier.  Many Precision's come with higher powered PSU's, plenty of good refurbs; XPS; and G5 Desktop: all of which can be Googled.  You'll find more power in certain XPS and Precision models, as G5 [5090] can't take any of the SUPER GPU models.