In the English Grammar Profile, C1 point 62 in ADVERBS/modifiers is defined:
(simply, truly, surely, apparently, naturally, surprisingly, inevitably, literally, exceptionally, frankly, clearly, amazingly, wisely, admittedly) to indicate an attitude or viewpoint, often in clause initial position.
For example:
She simply wrote down what was happening to her and her family about her confinement, and in doing so,
we have a very intimate record of this family during one of the worst periods of our world‘s history.
This grammar point is also related to ‘comment adverbials‘ and is often more than just one word. An Adverb + enough is common in this position and with this usage.
An iWeb search for these stance adverbs only in the initial position is very different to any position in the sentence. For example, there are over 2 million examples of ‘simply’ anywhere, but only a few thousand in the initial position:
1 . APPARENTLY , 30059
Apparently, he’s a poet.
2 . NATURALLY, 27766
Naturally, I was charmed by what you wrote about me.
3 . CLEARLY, 26259
4 . FRANKLY, 14964
5 . SURPRISINGLY, 14676
6 . ADMITTEDLY, 9653
7 . SURELY, 7023
8 . AMAZINGLY, 6144
9 . TRULY, 4979
10 . INEVITABLY, 4250
11 . LITERALLY, 3682
12 . SIMPLY, 3125
13 . WISELY, 340
14 . EXCEPTIONALLY, 227
*Some of these adverbs are sometimes used in other ways too, but they are all at B1 or higher, so the complexity range of adverb usage is high.
Here is an iWeb frequency list of just the vocabulary.
1 SIMPLY 2911337 (often followed by a negative verb phrase)
I simply don’t have time for this.
2 TRULY 1197042
3 CLEARLY 1118221
Clearly, he was not a man who minced words, nor should he have been.
4 APPARENTLY 592930
5 NATURALLY 558997
6 LITERALLY 548720
7 SURELY 374911
8 SURPRISINGLY 241096
9 FRANKLY 135921
10 INEVITABLY 118318
11 EXCEPTIONALLY 109343
12 AMAZINGLY 94722
13 ADMITTEDLY 71685
14 WISELY 70380
I’m simply the latest in a line that can be traced back generations.