I need to resize my sda4 to be able to install a program that needs quite much GB. I booted to my USB stick and tried Gparted but I couldn't make it to work resizing. I have an unallocated space of 3 GB I tried to use also with no luck. How to use this unallocated space for sda4? Or any other solution? I need at least 2 GB more.

I do not really understand what do you want. What would be the expected result?

That is very unlikely.
The swap can be enlarged, and/or the free area can be used as a second swap extent. Instead of telling us what you think you need, show us what the problem is - with messages.

I wonder if it's a tmpfs issue with /tmp - run this from a terminal on the system where you are trying the install.

/dev/sda3 ext4 39G 9,6G 27G 27% /
tmpfs tmpfs 3,9G 42M 3,8G 2% /dev/shm
tmpfs tmpfs 5,0M 4,0K 5,0M 1% /run/lock
tmpfs tmpfs 3,9G 0 3,9G 0% /sys/fs/cgroup
/dev/loop0 squashfs 128K 128K 0 100% /snap/bare/5
/dev/loop1 squashfs 254M 254M 0 100% /snap/brave/137
/dev/loop5 squashfs 66M 66M 0 100% /snap/gtk-common-themes/1515
/dev/loop3 squashfs 56M 56M 0 100% /snap/core18/2128
/dev/loop10 squashfs 33M 33M 0 100% /snap/snapd/12704
/dev/loop4 squashfs 56M 56M 0 100% /snap/core18/2253
/dev/loop9 squashfs 324M 324M 0 100% /snap/kde-frameworks-5-qt-5-15-core20/14
/dev/loop6 squashfs 66M 66M 0 100% /snap/gtk-common-themes/1519
/dev/loop2 squashfs 100M 100M 0 100% /snap/core/11993
/dev/loop7 squashfs 17M 17M 0 100% /snap/konversation/5
/dev/loop8 squashfs 51M 51M 0 100% /snap/snap-store/547
/dev/loop12 squashfs 33M 33M 0 100% /snap/snapd/13640
/dev/loop11 squashfs 219M 219M 0 100% /snap/gnome-3-34-1804/72
/dev/loop13 squashfs 62M 62M 0 100% /snap/core20/1242
/dev/loop14 squashfs 9,2M 9,2M 0 100% /snap/canonical-livepatch/119
/dev/sda1 vfat 197M 29M 169M 15% /boot/efi
/dev/loop15 squashfs 9,2M 9,2M 0 100% /snap/canonical-livepatch/126
tmpfs tmpfs 787M 28K 787M 1% /run/user/1000

Clarification, I'm trying to install a program that needs 27 GB but I need about 2 GB more to make it work.

swapoff the swap partition, then you can shrink/move over the swap partition to make room for sda3 to be increased in size. Be warned you may have booting problems by moving the beginning of sda3.

basically you may try to move your swap to the unallocated space and after that you may try to increase the size of sda3. But installing 27 GB onto your root partition may make your full system useless.

It worked by moving unallocated to swap and then shrinking swap and then resizing sda4. But that 27 GB is CS on Steam and I'm not overwhelmed doing it. An experiment with my son. It's just an old MacBook we're playing with. Thanks!