Hello Yashu, The last supported release of firmware for the EOSL AP7131 is v188.8.131.52 (service release). The radios do allow beacon interval to be set to 50, 100, or 200 (milliseconds) from AP Profile or Device level via Interfaces/Radios using UI or CLI.
WiNG 4 is not posted due to end of support for quite some time now. If you require a WiNG v4 firmware release, please have a support case generated and as long as the AP7131 is under contract/entitlement, we can provide the requested firmware. The last release was v4.4.2.