The IRE is short for Inter-Regio Express. This is a regional train.
If you have a one-country pass for Germany, it's not called a Eurail Pass, but a German Rail Pass. It is valid on ALL TRAINS in Germany, including the IRE, of course, with the exception of minor privately owned railways for tourists. The IRE trains (and all other regional trains) are covered by the Deutschland ticket as well.
The GRP comes in two varieties... the CONSECUTIVE-day pass, valid for a period of 3-15 consecutive days... or the FLEXI-version, which is valid for a specific number of travel days within one month.
Do you have a CONSECUTIVE-day pass? If so, you do not need the Deutschlandticket for trains since all possible travel is covered for every day of an entire month.
Sample consecutive-day pass: https://neet-log.com/wp/wp-content/uploads/2019/04/IMG_6321.jpg
Or do you have the FLEXI pass? If so, your pass is only valid on a specific number of days within a month, so you can only use it for 5 days, or 7 days, or whatever number of days your pass indicates, within your 30-day period.
Sample flexi-pass: https://fotoeins.files.wordpress.com/2017/09/grp_2017-spring2.jpg?w=1820&h=830
So if you have the flexi-version GRP, and if you intend to travel on more days than your GRP allows, you may in fact have a need to use the Deutschland-Ticket for train travel once you have run out of GRP travel days. The only hitch with the D-Ticket is that you cannot use it for high-speed trains... it's valid only on REGIONAL trains like the IRE, the RE, the RB, and others.
The D-Ticket will also be important for OTHER types of local transport within cities and transport authority districts... buses, subways, streetcars, etc. are NOT covered by the GRP. But with the D-Ticket in your pocket, it is possible to use these other local means within Munich, Berlin, and anywhere else you might need to use them.