Platform change at Buchloe station.

It will depend on how much luggage you are hauling and how quick you can exit and walk. Personally I would take an earlier train just to give you a little pad of extra time should go wrong.

Here is an earlier forum post on the subject-
https://community.ricksteves.com/travel-forum/to-the-west/buchloe-train-station

At Buchloe, platforms 4 and 5 are directly across from each other. So if the trains are on time, you'll disembark the first train, wait a couple minutes for the second train to arrive, and board.

That said, German trains have not been that punctual. I would consider an earlier train out of München given the time of day you'll be traveling in.

I assume you mean Immenstadt im Allgäu, not Immenstad.

Here is the track plan for the station in Buchloe. As mentioned above, a change from track 4 to track 5 is cross-platform change. If everything goes according to schedule, your train from Munich will get into Buchloe a minute before your connecting train from Augsburg arrives. My best advice is for you to keep track of the stops on the way to Buchloe and the times so you know when you are arriving in Buchloe. This is not an aircraft; you don't have to remain seated until the train stops in the station. When you know you are about to arrive, gather your luggage and move to the door, ready to get off when the train stops. Just walk across the platform. When your connecting train is boarding, the conductor will stand on the platform watching, and he (she) will not release the train while people are boarding.

Is this is enough time or should I jump on an earlier train from
Munich (I will catch the last from Buchloe so just want to be sure)?

This statement make be wonder. According the Bahn schedule website for Fri, March 3 and Sat, March 4, the last connection from Munich to Immenstadt with a change at Buchloe leaves Munich at 22:20 and changes in Buchloe from 23:03 to 23:07, getting into Immenstadt at 1 minute after midnight. Is that really the train that you are planning to take? Are you really planning to arrive in Immenstadt that late? I wouldn't even expect a hotel in Immenstadt to be open that late to take you.

Are you using the Bahn scheduling website, https://reiseauskunft.bahn.de/bin/query.exe/en? If not, what schedule website are you using and why are you not using the Bahn website?

And, the earlier train leaves Munich Hbf at 21:20 and goes directly to Immenstadt without a change in Buchloe, so you wouldn't have to worry about making the change.

What is your date of travel, and at what time to you want to arrive in Immenstadt?

That said, German trains have not been that punctual.

While this is regrettably true for long-distance traffic, it is not true for regional traffic, which is relevant here and still has a punctuality rate of over 90%. I often change trains in Buchloe (from / to Augsburg) and very rarely have problems. Many people will change from the train from Munich to the one to Immenstadt, so the latter will certainly also wait a few minutes.

If the train you are connecting to is the last train to Immenstad it will wait for a delayed train from Munich. DB does not like having to pay for taxis for passengers that missed connections...