Mission and airfield building is a worthwhile pastime.
What modpack are you using? Details may differ.
Do you know that M4T has a specific section for "templates" of all kinds? Numerous have "spec built" airfields in random areas (namely Kurfurst's) which you can use whole or in parts for your own needs.
https://www.mission4today.com/index.php?name=Downloads&c=95I am trying to model a WW2 makeshift dug up air strip on random terrain, where I can have ai aircraft take off from and land at.
I can find generally even terrain, but I've run into problems with creating an airstrip that can have planes land on it because they have to be set to land at something with an air field icon or aircraft carrier.
That's the correct solution, the auxiliary airfields in the static ships.
They are like a "carrier deck" which can be placed anywhere on flat ground. The operations can work like on a static carrier, but you are not forced to use it like that, depending what you want to do and which plate (small or very wide) you are using.
In no case can you or AI taxi over the edge of such a plate, it will cause a crash.
I can make aircraft take off with no problem on any terrain that is generally level without having to be on a test runway with setting them to taxi and then to take off in the direction I want. They roll on the terrain just fine.
AI can take off anywhere "flat" but player can't.
Airfields are (usually!) flattened in the map building phase, every other "regular" terrain is very bumpy, even if it appears flat (realistic take-off makes you feel this, if turned off, you won't feel it, but you will also not collide with ground at all)
There once was a mod called Zuti's friction mod, somewhere under 4.10. It became incompatible to 4.12 game versions. If a map was built by someone using this, it can be that airfields are not properly treated and now bumpy as hell without the mod. In this case also an invisible auxiliary "ship" saves the day to "flatten the place" (They should be called Seabee objects really....

). The airfield positions can still be used normally, no forced use of the "carrier" runway point.
On such an auxiliary plate, you never *have to* attach the carrier point to take off if you do not want to!
You can always make planes take off by using "taxi to take off" waypoints to line them up initially (under any 4.12 based game)
I understand your main problem now is landing.
That is a bit uncomfortable, as here *only* the auxiliary carrier strip attachment gets you a well defined result. After stop, the planes will "disappear", just like on a carrier, no taxi to parking.
You can use several aux strips on top of each other. One big invisible base to flatten the take off area -> take off by taxi and such
Another small invisible strip and there an attached landing, that defines the landing strip, should the big plate have to be positiond "off-line".