Question - is there any custom android OS for converting old phone into mifi modem? (opens in new tab)

hi, if this is wrong sub, please enlighten me. like the title says. i have some 5G phone that already obselete for day to day use. on the other hand, im searching a good mifi modem to use for my traveling. so is there any custom android OS that so simple or striped down. that only function as...