Does Intel offer write-once FPGA or an equivalent product?

April 1st, right?

A write once FPGA is basically called an ASIC. And yes, Intel does ASICs...

https://www.intel.com/content/www/us/en/foundry/overview.html

Write once (antifuse based) FPGA or CPLD devices are not very common anymore.

Intel/Altera does offer devices (MAX, MAX2, MAX5, MAX10 series for example) that store the configuration in internal EEPROM cells so they are basically instant on, and don't need to load a configuration serially from an external EEPROM device.

They are not write once, they can be reprogrammed hundreds of times. They do offer security fuse protection to prevent readback.