as you know in opencart 4.x version there is onepage checkout and only login link and when you click on login link it goes to login page after complete refresh page and then you login and again have to come on checkout page after click again.
its so much irritating

This extension has solved this problem, you can login on checkout page rather goes anywhere
You have two options from admin
I) Login popup
II) Login radio buttion
you can see screenshots images or can see demo link

DEMO 4.x
add any item in cart and click on checkout page and click on login



Installation on 4.x

Step1: extract zip file
Step2: extract vqmod2.6.7.ocmod.zip file
Step3: upload "vqmod" folder directly via ftp or file manager
Step4: open link www.yoursitename/vqmod/install
Step5: write your admin directory link if change otherwise remain it as it is admin.
Step6: Login to admin and Install extension logincheckout.ocmod.zip

if have any issue please email me at dyisolco@gmail.com