I’ve had it with this crap. Reflection probes and a bunch of other stuff doesn’t work on 2020.3.3f1 LTS! i was told to update to the latest fix version which is f17 for 2020.3 after the update, the entire scene is pink and the console says all the shaders failed to compile. Errors like “not fully initialized”. how the hell did they work in the last fix?? and how Am I supposed to fix that??? I buy shaders fromthe asset store and they say they support the lastest version of Unity so what the hell am i missing here? the only reason I buy shaders is because i dont understand the code. how the hell is this a “FIX” unity? huh?
Which render pipeline are you using?
URP 10.3 I finally got an answer in that you have to purge all your packages and reimport them in safe mode. I just wish these things were a bit more intuitive. Though after upgrading i’m not too happy that reflection probes are still baking black.
2020.3.3f1 uses api 10.4.0
any shaders made in 10x should also work in 11x
they may also work in 12x beta / Alpha but with risk limited to forward render only
Note
shaders made in 7x pre 7.3.1 will only work in 7x
shaders made in 7x 7.3.1 or higher should also work in 8x
shaders made in 7x that had Xbox one support will not work in 8x
shaders made in 8x or 7x will not work in 10x or anything higher
Id like to try going to URP 11 and see if then i can finally use reflection probes.
Which packages are you referring to?
I just updated to 2021.2.6 \ 2021.2.7 too… pink URP shaders everywhere… 
Check whether your render pipeline asset is still assigned in the graphics (and quality) settings. For some reason they get removed there on version upgrade every time. I have a script that automatically reassign them for that purpose.