Every time you drop a hammer or something you will damage the floor.
Can you level a floor with mortar.
Leveling using mortar is not acceptable in so many ways but most important one is that it would crack.
No a mortar can be used to blow a big hole in a floor if you are accurate enough.
Can a mortar be used to level a floor.
Even if it doesn t crack and it will you will have a problem because it is workshop.
Thinsets indeed can crack if it s too thick and also they are not very strong don t withstand compaction as well as ordinary mortar and so there indeed is a chance that you have tiles cracking after thinset applied too thick.
Your concern about self leveling is justified if mixed thin enough to flow properly it will find any crack or opening to run through also do not use regular mortar to bed the backer board use thin set.
Do not use mortar use floor patch.
If you just have 2ft x 3ft there s no problem using usual not thin set mortar to level the surface it will be cheap likely cheaper that self leveling concrete and quite easy to do.
This is not the same as self leveling and is screeded or troweled into the low spots to fill them.
A sand and cement screed which isn t exactly mortar as there isn t enough moisture in it to make it mortar can be used to.