I created this document with the diff between REL1_35 and master.

https://docs.google.com/spreadsheets/d/1_vrhhz2PI7aLEFxzeVFtot7XsF764wrD6uQM_xK94Qw/edit?usp=sharing

After a scroll through I only suggest these two, not really high impact but bug fixes that improves the release.

Bug fix for null-checking Title:newFromText
https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/621474

Bug fix for redirected links in mediawiki do not automatically redirect the user to
the merged item. In wikibase it does, they should not differ.
https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/618988

I guess the reviewer should decide if this is valid, then we add the list of backports.

The above look good to me. I also just went through git log --no-merges origin/REL1_35..origin/master and found the following that looked interesting:
(in no particular order)

a5d67722354ff3c537d30dfb90f42b37df51f3d0
07885b932ca3dc5ecd80f2272d9cc6085f1b6b8a
084588cb05181d19d1fc36672b6fa4532180b6e8
ec73b2bad42312fe2697a4c65c3aa54be61383ac
4bc7be4c8508e564fde4af9772d73516f3e9fdea
0adc27077904c9c780649544f047c69f47b49407
3479875548cbe285541dd75d48274e9c10116aaf
ab757a7660eba62f6074580faa2f3d0d3bfbe217
b435e34aac72540f90ec4f2f0d1798ec174d956c
2cfceb27e5023af0782993797524fe6de2c3738f (relevant core change might be backported also, see https://gerrit.wikimedia.org/r/c/mediawiki/core/+/667823)
ccbf70597cb1493135ccbdbcf38d2e17849c8b93
6e09365fc0599b283c0998190bc6d2dfbd195c00
3b60c64e862c7c5956ea8a02f2190c212dcf2f4a
7c255f84bcd7a1349fbd491b1bab0b25340b0804

https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/672590
https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/672650

a5d67722354ff3c537d30dfb90f42b37df51f3d0 ok - https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/672591
07885b932ca3dc5ecd80f2272d9cc6085f1b6b8a <------------------ already in REL1_35
084588cb05181d19d1fc36672b6fa4532180b6e8 ok https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/672592
ec73b2bad42312fe2697a4c65c3aa54be61383ac <----- hard to merge
4bc7be4c8508e564fde4af9772d73516f3e9fdea ok https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/672593
0adc27077904c9c780649544f047c69f47b49407 ok https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/672594
3479875548cbe285541dd75d48274e9c10116aaf ok https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/672595
ab757a7660eba62f6074580faa2f3d0d3bfbe217 <--- hard to merge
b435e34aac72540f90ec4f2f0d1798ec174d956c ok https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/672596
2cfceb27e5023af0782993797524fe6de2c3738f <--- this is only improving the performance of tests, do we care?
ccbf70597cb1493135ccbdbcf38d2e17849c8b93 ok <--- https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/672662/1, https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/649362/3
6e09365fc0599b283c0998190bc6d2dfbd195c00 <--- hard to merge
3b60c64e862c7c5956ea8a02f2190c212dcf2f4a <--- hard to merge
7c255f84bcd7a1349fbd491b1bab0b25340b0804 <--- already in REL1_35

In T275866#6916597, @toan wrote:

2cfceb27e5023af0782993797524fe6de2c3738f <--- this is only improving the performance of tests, do we care?

Per T270353: Wikibase client Scribunto tests fail due to ParserOptions-option handling change it also fixes the tests (once the other patch is applied, which might happen to REL1_35, as noted above).

I just +2ed all remaining patches. I suggest we go over the ones that are harder to backport with @Samantha_Alipio_WMDE and decide which ones are worthwhile doing.

In T275866#6919361, @hoo wrote:

In T275866#6916597, @toan wrote:

2cfceb27e5023af0782993797524fe6de2c3738f <--- this is only improving the performance of tests, do we care?

Per T270353: Wikibase client Scribunto tests fail due to ParserOptions-option handling change it also fixes the tests (once the other patch is applied, which might happen to REL1_35, as noted above).

Ah you are on point! Cherry picked this one aswell!

all the easy stuff merged lets review the other stuff together!

Ok after a quick chat we decided to give the other backports proper attempt before discarding any.

ec73b2bad42312fe2697a4c65c3aa54be61383ac ---- we can skip this one because it's fixing an error in a refactoring from the decoupling hike that is not included in REL1_35 T257447
ab757a7660eba62f6074580faa2f3d0d3bfbe217 ---- we can skip this as well as the other two patches that fixes the original issue already has been backported. This changeset was used to identify the origin of the problem.

6e09365fc0599b283c0998190bc6d2dfbd195c00 --- https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/673277/1 required a previous patch for SubmitEntityAction
3b60c64e862c7c5956ea8a02f2190c212dcf2f4a ----- https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/673282

Should re-run tests & pass once https://phabricator.wikimedia.org/T277750 is done

And reminder: once merged we need to update the release notes.

@Samantha_Alipio_WMDE Do we also want 97fb57717b5c858d41df60842475958fef905e1e (fixes undoing changes that turn entities from redirects into normal entities again, thus making them redirects again)?

I just +2ed the last backports here, and except for the question posed above and the missing release notes, this is done.

With 97fb57717b5c858d41df60842475958fef905e1e merged, I take this investigation could be concluded.