Checked with both Zephira's test and my own addon on Win 1.16.1 release. I confirm the issue is present as described. No errors logged, however the recipe for a custom block or item is not available to the user in creative menu nor suggested in the survival crafting bench menu when ingredients are available. Only vanilla recipes are available. (I did note that a custom entity's spawn egg remains available in creative mode, so that bit is not broken! I also tested with experimental gameplay switch on - no difference to behaviour.)
Checked with both Zephira's test and my own addon on Win 1.16.1 release. I confirm the issue is present as described. No errors logged, however the recipe for a custom block or item is not available to the user in creative menu nor suggested in the survival crafting bench menu when ingredients are available. Only vanilla recipes are available. (I did note that a custom entity's spawn egg remains available in creative mode, so that bit is not broken! I also tested with experimental gameplay switch on - no difference to behaviour.)