Easiest would be a 300 ohm dipole, attached to the correct connections on the rear panel.
$6.99 at Amazon:
https://www.amazon.com/Bingfu-Terminal-Bluetooth-Receiver-Amplifier/dp/B07MG2XYR6/
Is this like the one you use?
The basic FM antenna that was included with most receivers was called a 300 ohm dipole.
This one is on Amazon for about seven dollars:
https://www.amazon.com/Bingfu-Terminal-Bluetooth-Receiver-Amplifier/dp/B07MG2XYR6
I recently purchased a vintage Sony receiver by which the FM antenna connects via two exposed wires (just like speaker wire connects). I've never had one like this before. If I were to purchase a regular wire dipole antenna that has metal prongs on the two ends (like the one found at the link below), could I simply remove those prongs, strip it down to the exposed wire, and insert them?