I've been in the exact same scenario twice and what I've learned is that internal tools (especially in big companies) only get "deprecated" but it's hard to abandon them completely.
I've found the decision to "deprecate" tools, especially long established ones, comes along with political shenanigans and especially so when the tool is used by multiple teams with competing interests. One team usually can yell louder than all the other teams and force the new tool to be very specific to their workflow, but because other teams have different workflows the new tool won't work for them. So you're in this limbo of supporting both forever until everyone can agree to switch to the new tool or someone important enough decides to completely turn off the deprecated tool.
I've found the decision to "deprecate" tools, especially long established ones, comes along with political shenanigans and especially so when the tool is used by multiple teams with competing interests. One team usually can yell louder than all the other teams and force the new tool to be very specific to their workflow, but because other teams have different workflows the new tool won't work for them. So you're in this limbo of supporting both forever until everyone can agree to switch to the new tool or someone important enough decides to completely turn off the deprecated tool.