Samsung S21 FE was released many years back. And someone has now ported Galaxy S25 Edge ROM onto the S21FE, giving you latest Galaxy AI features and other goodies that the S25 users enjoy. This ROM is debloated, no unnecessary apps.
This Samsung S25 ROM for S21FE also gives you latest One UI 8. If you model number ends with SM-XXXXB2/DS or non DS, flash this otherwise flash this.
To flash this S25 ROM, you will have to get hold of S21FE’s TWRP. Then, copy the ROM to root of your phone’s storage. Fire up TWRP by holding volume up and power button on your S21FE and then browse for file you downloaded earlier and flash it in TWRP. Once that is done, we highly recommend you format the phone using one of the options in S21FE’s TWRP.
Everything is working out of box, including fingerprint scanner, which usually does not work after flashing a 3rd party ROM on any android phone.
Since you will have to install TWRP on S21FE to install this ROM, you will lose warranty. Just keep that in mind before you install this ROM. Also, backup your data as all will be lost after installing it.