Ubuntu 20.04 Radeon HD 7670M - DRI_PRIME=1 glxgears doesn't work

I have an old laptop with a Radeon HD 7670M GPU card which i want to use. I read lot of topics on this site and i tried different solutions:

First of all i installed ubuntu 14.04 and the fglrx driver which works perfectly. The problem here is that its a very old OS which make very hard to use most of the modern program versions like wine.

I decided to try with the ubuntu 20.04 but the problem is that my GPU is not supported anymore by ATI and to use the open driver which is already included in ubuntu 20.04.

After a fresh install of the OS i tried to check if the GPU works by doing:

DRI_PRIME=1 glxgears

but i received this error:

radeon: Failed to allocate a buffer:
radeon:    size      : 524288 bytes
radeon:    alignment : 4096 bytes
radeon:    domains   : 2
radeon:    flags     : 4
radeon: Failed to allocate a buffer:
radeon:    size      : 524288 bytes
radeon:    alignment : 4096 bytes
radeon:    domains   : 2
radeon:    flags     : 4
radeon: Failed to allocate a buffer:
radeon:    size      : 4096 bytes
radeon:    alignment : 4096 bytes
radeon:    domains   : 2
radeon:    flags     : 0
radeon: Failed to allocate a buffer:
radeon:    size      : 4096 bytes
radeon:    alignment : 4096 bytes
radeon:    domains   : 2
radeon:    flags     : 0
radeon: The kernel rejected CS, see dmesg for more information (-16).
X Error of failed request:  BadAlloc (insufficient resources for operation)
  Major opcode of failed request:  149 ()
  Minor opcode of failed request:  2
  Serial number of failed request:  42
  Current serial number in output stream:  43

How can i try to solve this? There are lot of days that i have this problem trying to solve it.

Thank you in advance for your answer, ask me if you need to know more.