After installation of Debian sid or MintPPC, there is no wireless support out of the box anymore for airport. I will explain why this is. In the past I installed two different drivers for airport at the same time. I have noticed that it is better to have only one installed. The problem however is that not every PowerPC Mac has the same airport cards. The cards may vary in the chipset Apple used. It is therefore advizable to first find out what chipset is used in your machine. Do the following:

lspci -nn -d 14e4:

Then look in the following table, which driver needs to be installed, either b43 or b43legacy.
In my computer, a PowerBook G4 Aluminium, the output is 14e4:4320. Furthermore it says BCM4306 rev 2. The Table says that the b43legacy driver should be used. It indeed works well for me.
On my newer model PowerBook G4 I get 14e4:4320 BCM4306 rev 3. On this machine b43 works well.

Please look carefully at device ID and chipset name.

PCI-IDSupported?Chip IDModesPHY versionAlternative
14e4:0576not testedBCM43224a/b/g/n?brcm80211
14e4:4301yes (b43legacy)BCM4301bB
14e4:4306yes (b43legacy)BCM4306/2b/gG
14e4:4312yesBCM4311a/b/gG (r8)wl
14e4:4313not testedBCM4311a?wl
noBCM4313b/g/nLCN (r1)brcm80211
14e4:4315yesBCM4312b/gLP (r1)wl
14e4:4318yesBCM4318b/gG (r7)
14e4:4320yes (b43legacy)BCM4306/2b/gG (r1)
yesBCM4306/3?G (r2)
14e4:4321partiallyBCM4321?N (r2)
14e4:4322yes (3.18+)BCM4322b/g/nN (r4)
14e4:4324yes (b43legacy)BCM4306a/b/gG (r1)
yesBCM4306/3a/b/gG (r5)
14e4:4325yes (b43legacy)BCM4306/2b/gG (r1)
14e4:4328partiallyBCM4321a/b/g/nN (r2)wl
14e4:4329partiallyBCM4321b/g/nN (r1)wl
14e4:432anot testedBCM4321a/nNwl
14e4:432bpartiallyBCM4322a/b/g/nN (r4)wl
14e4:432dnot testedBCM4322a/nNwl
14e4:4331yes (3.2-rc3+)BCM4331a/b/g/nHT (r1)wl
14e4:4350yes (3.8+)BCM43222a/b/g/nN (r6)
14e4:4353yes (3.1+)BCM43224a/b/g/nN (r6)wl/brcm80211
14e4:4357yes (3.1+)BCM43225b/g/nN (r6)wl/brcm80211
14e4:4358yes (3.17+)BCM43227b/g/nN (r16)wl
14e4:4359yes (3.17+)BCM43228a/b/g/nN (r16)wl
14e4:4360noBCM4360?AC (r1)
14e4:4365noBCM43142b/g/nLCN40 (r3)wl
14e4:43a9yes (3.17+)BCM43217b/g/nN (r17)
14e4:43aayes (3.17+)BCM43131b/g/nN (r17)
14e4:43b1noBCM4352a/b/g/n/acAC (r3)
14e4:4727noBCM4313b/g/nLCN (r1)wl/brcm80211
14e4:a8d6not testedBCM43222?N (6)
14e4:a8d8yes (3.6+)BCM43224a/b/g/nN (r6)brcm80211
yes (3.6+)BCM43225?N (r6)brcm80211
14e4:a8dbpartially (3.18+)BCM43217b/g/nN (r17)
14e4:a99dnot testedBCM43421???

To install the b43 driver do the following (make sure you have the MintPPC repos in /etc/apt/sources.list):
sudo apt update
sudo apt install firmware-b43-installer

To install the b43legacy driver:
sudo apt update
sudo apt install firmware-b43legacy-installer

To make use of the driver a reboot is necessary.

If you have a recently installed MintPPC system, you will have both packages installed. Both packages are taken directly from Debian and are not well suitable for Airport cards. I included versions with old source code which work well for Airport cards. In case you have both versions installed, you have to first delete both of them:
sudo apt remove firmware-b43-installer firmware-b43legacy-installer b43-fwcutter
Then install one of the drivers as mentioned above.

Make sure that you pin one of these programs. You can have a look at how lxpanel and lxpanel-data are pinned. Just do the same for the airport driver.

link to lxpanel